HEAT oven to 400°F.
BROWN meat in large nonstick skillet on medium-high heat. Add yellow onions; cook and stir 5 min. Stir in soup; cook 3 min. or until heated through, stirring frequently. Spoon into 2-L baking dish sprayed with cooking spray.
BEAT egg and milk in medium bowl with whisk until blended. Stir in cheese and green onions. Add baking mix; stir just until moistened. Drop by spoonfuls over meat mixture.
BAKE 35 min. or until biscuits are golden brown and casserole is heated through.
serving size = 1/4 recipe (331 g)