The Lunch Song is a song from "The Castle", as seen in a promo for the show.
Lyrics
Gumball: Boom-A!!
Gumball: We home alone with Dad so I make me own lunch.
I can eat what I want so I take the best munch.
I pick up ham and chocolate chips and stick 'em in the bread.
It need a little sauce, I say maple and red.
Darwin and Anais: Boom!