[I]s my consumption of Rotini with meat sauce on Friday during Lent a mortal sin for me, or only for my Catholic neighbors? Is Lent more like Ramadan or the Jewish Sabbath?Lent is not exactly like Ramadan nor the Jewish Sabbath.
Lenten observance is governed by Canon Law. Catholics are obliged to observe Lent in accordance with Canon Law because Catholics are obliged to obey the Church. Because non-Catholics are not subject to Canon Law, they are not bound to the observance of Lent (although they certainly might profit from such an observance if done with proper intent):
Merely ecclesiastical laws bind those who have been baptized in the Catholic Church or received into it, possess the efficient use of reason, and, unless the law expressly provides otherwise, have completed seven years of age (Code of Canon Law, Title I, Canon 11).Hence non-Catholics are not bound to observe Lent (although the case is different, as far as I know, for Catholics who leave the Church; they would still be bound to this (among other things) unless canon law says otherwise someplace).
Canon Law says this about days of penance:
Can. 1249 The divine law binds all the Christian faithful to do penance each in his or her own way. In order for all to be united among themselves by some common observance of penance, however, penitential days are prescribed on which the Christian faithful devote themselves in a special way to prayer, perform works of piety and charity, and deny themselves by fulfilling their own obligations more faithfully and especially by observing fast and abstinence, according to the norm of the following canons.Note that canon 1253 grants a conference of bishops (as, for example, the USCCB) the authority to modify these obligations somewhat. The USCCB has done so:
Can. 1250 The penitential days and times in the universal Church are every Friday of the whole year and the season of Lent.
Can. 1251 Abstinence from meat, or from some other food as determined by the Episcopal Conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday.
Can. 1252 The law of abstinence binds those who have completed their fourteenth year. The law of fasting binds those who have attained their majority, until the beginning of their sixtieth year. Pastors of souls and parents are to ensure that even those who by reason of their age are not bound by the law of fasting and abstinence, are taught the true meaning of penance.
Can. 1253 The conference of bishops can determine more precisely the observance of fast and abstinence as well as substitute other forms of penance, especially works of charity and exercises of piety, in whole or in part, for abstinence and fast.
Fridays During Lent—In the United States, the tradition of abstaining from meat on each Friday during Lent is maintained.That same page goes on to describe a variety of penitential practices which may be substituted for abstaining from meat on Fridays outside of Lent.
Fridays Throughout the Year—In memory of Christ's suffering and death, the Church prescribes making each Friday throughout the year a penitential day. All of us are urged to prepare appropriately for that weekly Easter that comes with each Sunday.
Anyway, there are two points here: first, in canon law the Church has ordained that Catholics must abstain from meat during Lent, subject to amendment by the regional conference of bishops; second, the USCCB has modified this so that abstinence from meat during Lent is only obligatory on Fridays. The reason I make the second point is to identify the reason for the difference between the American observance of Lent and what is specified in canon law.
Violation of canon law is not a mortal sin per se, if by that it is meant that it would necessarily be a sin to do something forbidden by canon law if the Church had not made a law concerning it. Hence if there were no laws concerning observance of Lent, failure to observe it would not be a mortal sin; on the other hand, the fact that there are canons regarding the sacraments is not why we have sacraments, which were ordained by the Lord. What makes deliberate, willful, knowing violation of canon law a mortal sin is the duty that Catholics have to obey the Church. So if your Catholic neighbor fails to observe Lent properly, this might not be a mortal sin if he does so in ignorance of his duty (due to poor catechesis, for example) or if he does so without deliberately, willfully, and knowingly intending to disobey the Church. In any case, it could not be a mortal sin for a non-Catholic to ignore Lenten observance, since he is not bound by canon law.