The menu:[1]

It is not customary to serve bread for this meal [as it takes place after the Friday night meal in which everyone already ate bread and recited Birchas Hamazon].[2] It is customary to serve Mezonos products as well as fruits[3], as well as nuts[4] and legumes, including lentils.[5] It is customary to serve the legumes prior to serving the fruits.[6] [Today the custom is to serve chickpeas[7], alcoholic beverages, and beer by the Shalom Zachar.]

[1] Shevach Habris 10:4

[2] However, see Sefer Hasichos 5703 p. 154 “On Erev Shabbos Shuva of the year 5550, the Alter Rebbe announced that he is inviting all of the members of the city and guests to a Shalom Zachar meal on behalf of his newborn grandson. The family and about 30 guests of the elder Chassidim were invited to wash their hands for the meal, while everyone else was invited to they finished their meal prior to reciting Birchas Hamazon, in which they would join in the eating of beans and lentils and then join the Zimun. The meal would take place in the large Shul in the courtyard.”

[3] See Rama Y.D. 265 in end; Chavos Yair 70; Migdal Oz Beginning of Hilchos Mila; Tehila Ledavid [Butchach] on Tehillim 104:14; Aruch Hashulchan 265:37

[4] See Tehila Ledavid ibid; Koreis Habris 265:68

The reason for eating nuts: The reason for eating nuts is because there is a verse in Shir Hashirim 6:17 which connects the Egoz to the Mitzvah of circumcision. [Otzer Habris 2:6]

[5] See Luach Birchas Hanehnin 3:16 “Therefore it is accustomed to first serve legumes by the meal which takes place for the birth of a son”; Tehila Ledavid ibid; Koreis Habris 265:68

The reason for eating lentils: The reason that lentils are served is because lentils is a food served to a mourner and according to some opinions [i.e. Taz 265], the reason behind this meal is in order to comfort the soul of the child who forgot all of his Torah learning after leaving his mother’s womb. [Koreis Habris 265:68 based on Derisha ibid] Alternatively, the reason is because lentils is a food of joy. [Tehila Ledavid ibid in name of Midrash Raba Toldos 63:19]

[6] See Luach Birchas Hanehnin 3:16 “Therefore it is accustomed to first serve legumes by the meal which takes place for the birth of a son”; See Shevach Habris 10 footnote 10 for a lengthy explanation by Rav M. Ashkenazi a”h.

[7] Shevach Habris 10:4