1. Brown beef in a large nonstick skillet over medium-high heat, stirring often, 10 minutes or until meat crumbles and is no longer pink. Remove ground beef from skillet using a slotted spoon; reserve 2 Tbsp. drippings in skillet. Reduce heat to medium.
2. Sauté onion, mushrooms, and garlic in hot drippings over medium heat 10 to 11 minutes or until tender. Stir in ground beef, peas, and next 4 ingredients. Sprinkle flour over meat mixture. Increase heat to medium-high, and cook, stirring constantly, 1 minute. Stir in tomatoes, bay leaf, and vinegar, breaking up large tomato pieces with a spoon. Reduce heat to medium, and cook, stirring often, 3 minutes or until slightly thickened. Remove bay leaf. Transfer mixture to a lightly greased 3-qt. baking dish or pan. Spoon Cheese-and-Carrot Mashed Potatoes evenly over meat mixture, smoothing with back of spoon.
3. Bake at 400° for 15 minutes or until thoroughly heated. Let stand 5 minutes before serving.
Note: To make ahead, prepare recipe as directed through Step 2. Cover tightly with aluminum foil. Freeze up to 1 month. Thaw in refrigerator 24 hours. Bake at 400° for 40 minutes or until thoroughly heated, shielding with aluminum foil after 25 minutes to prevent excessive browning.