Combine the first 3 ingredients in a bowl; stir well. Gradually add water and next 2 ingredients, stirring with a wire whisk until blended; set aside.
Cook the onion and beef in a large saucepan coated with cooking spray over medium-high heat until browned, stirring to crumble; drain in a colander.
Return beef mixture to pan. Add parsley and next 5 ingredients; stir well. Add broth mixture; cook over medium heat for 15 minutes or until thickened, stirring constantly.
Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray. Carefully split biscuits in half horizontally, and place over beef mixture. Bake at 400° for 10 minutes or until biscuits are lightly browned.
Make-Ahead Tips: You can assemble the casserole ahead of time, without thawing the frozen vegetable and omitting the biscuits; cover and freeze. Thaw frozen casserole overnight in refrigerator; let stand at room temperture 30 minutes. Top with biscuits; bake as directed.