Green’s Dictionary of Slang

(US) a dish of peas or beans.

1923		El Paso Herald (TX) 31 Jan. 8/2: ‘Thousand on a plate’ is the most universal phrase for pork and beans.
1935		A.J. Pollock Und. Speaks.
1942		Z.N. Hurston ‘Story in Harlem Sl.’ in Novels and Stories (1995) 1002: Jelly figured that if he bullskated just right, he might confidence Sweet Back out of a thousand on a plate.
1954		Ames (IA) Daily Trib. 11 Dec. 1/1: Your waitress is not talking to her bookie when she yells ‘1000 on a plate.’ Those are your baked beans, of course.
2003		The ‘Old’ Oxford Menu at The Oxford Saloon & Cafe Established 1883 🌐 ‘Thousand on a Plate’ Baked Beans.