The Mitzvah of having a meal on Purim is specifically in the daytime and the Shulhan Aruch (Orah Haim 695:1) rules that one who does so on the night of Purim does not fulfill one’s obligation. Nevertheless, the Rama (ibid.) writes that one should still have a meal and rejoice on Purim night. The Magen Avraham (where?) cites opinions that hold that one fulfils one’s obligation at night, but this is not the normative Halalcha.
The Poskim discuss whether or not there is an obligation to specifically have bread with the Purim meal. One practical implication of this question is whether or not one would need to repeat Birkat Hamazon if one forgot to insert “Al HaNissim”. Generally speaking, whenever a meal is obligatory, any additions to Birkat Hamazon related to that obligation (like Shabbat, Yom Tov) are also obligatory. The Maharshal (Yam Shel Shlomo) rules that there is an obligation to have bread, and therefore if one had a bread-based meal on Purim and forgot “Al HaNissim”, one would have to repeat Birkat Hamazon. The general consensus, however, is that one still fulfills one’s obligation of the Purim meal even if one did not eat bread. It is noteworthy that Rabbi Ben Zion Abba Shaul (Or LeZion, vol.) writes that the ideal way to perform the Mitzvah of the Purim meal is to include bread, and thus if one is able to one should eat bread.
It should also be noted that even if the Purim meal extends into the night and, the Shulhan Aruch (Orah Haim 695:3) rules that one must still recite “Al Hanissim” in Birkat Hamazon.
Summary: Although one fulfills one’s obligation of Seudat Purim even if one does not eat bread, one should ideally eat bread if possible.