^ 9.The mitzva to eat a se’uda is elaborated upon in Megilla 7b. By eating a meal, one fulfills the injunction of the verse, "To observe them as days of feasting and joy" (Esther 9:22). While it is true that the Sages derive from here that one may not fast or deliver eulogies on Purim (Megilla 5b), there is certainly also a mitzva to rejoice actively, which one accomplishes by partaking in a joyous meal. So explains Shibolei Ha-leket §201. (Some maintain that the festive meal is a rabbinic mitzva; Binyan Shlomo §58 discusses this.) The mitzva includes eating meat and drinking wine, which is why SA 696:7 rules that even an onen (a mourner whose deceased relative has not yet been buried) must observe it.
According to Rambam (MT, Laws of Megilla 2:14), Rashba, and Ritva (Megilla 4a), the mitzva of eating and drinking is only during the day, as the verse in Esther says "days." MA 695:6 cites Kol Bo as stating that some have a custom not to eat meat at night, so as not to mistakenly think that this counts as the Purim meal. On the other hand, Raavya maintains that one must have a meal with meat and wine at night, just as it is a mitzva to read the Megilla at night in addition to the main reading of the day. The only difference is that the main, more dignified meal must take place during the day. Baĥ concurs. Tosafot (Megilla 4a) also seem to agree that there is a mitzva to have a festive meal at night as well. Rema 695:1 rules similarly in the name of Mahari Brin, as do MB ad loc. 3, Kaf Ha-ĥayim 695:4. Either way, it is clear, according to the simple understanding of the issue, that one enhances the mitzva by engaging in all types of joyous activities throughout the day, as is customary.
^ 10.It is a mitzva to make an elaborate Purim meal, as Rambam, Tur, and Rema state. It seems that according to these authorities, the meal should be even more elaborate than a Yom Tov meal. The term "joy" includes eating meat and drinking wine, as the Sages state in Pesaĥim 109a regarding Yom Tov. Even though the obligation to eat meat on Yom Tov used to relate specifically to the meat of a peace offering (shelamim), there is nonetheless a mitzva to eat meat on Yom Tov even after the destruction of the Temple, since doing so makes one happy, as SAH 529:7 and BHL 529:2 explain. See Yeĥaveh Da’at 6:33. Eating chicken also brings joy, as the Gemara and Tosafot in Beitza 10b indicate.
The poskim disagree about whether one must eat bread at the Purim meal. According to Me’iri, Raavya, Maharshal, and Mor U-ketzi’a, one must eat bread, just as it is a mitzva to rejoice on Yom Tov and to eat bread at the meals. Terumat Ha-deshen and MA 695:9 maintain that one does not need to eat bread. They explain that the obligation to eat bread on Yom Tov is not based on the obligation to rejoice, but on the concept of honoring Yom Tov, which the Torah calls, "sacred occasions" (Vayikra 23:4). They similarly disagree about one who forgot to recite Al Ha-nisim in Birkat Ha-mazon (see above ch. 15 n. 19). Nevertheless, MB 695:12 states that one should not repeat Birkat Ha-mazon, since we are lenient in cases of uncertainty about berakhot, and AHS 695:7, 12 rules, on the one hand, that it is a mitzva to eat bread at the Purim meal, but on the other hand, one who forgets Al Ha-nisim does not need to repeat Birkat Ha-mazon, as the obligation to recite Al Ha-nisim in Birkat Ha-mazon cannot be more stringent than the obligation to recite it in the Amida. See Yeĥaveh Da’at 6:89.