Pre heat over to 425°F Coat 1 1/2 baking dish with cooking spray. In a large non stick skillet, cook boof and onion over med heat until beef is brown and onion is tender, 5 minutes. Drain excess fat. Stir in Sloppy Joe sauce; cook until heated through;remove from heat. Reserve 1/3 cup Mexi corn;stir remaining into beef mixture;transfer to baking dish. Stir baking mix, 1/2 C cheese, and 1/3 C water, into reserved Mexi corn;dollop spoonfuls over beef mixture.
Bake 15 - 20 minutes or until biscuits are golden, sprinkling with remaining 1/4 C cheese during last 2 minutes of cooking. Cool 10 minutes. If desired, sprinkle with 1 scallion, sliced.