Preheat oven to 350°F. Grease a 9x13 casserole dish.
Mix sour cream, mayonnaise, and 4 ounces of cheese together, set aside.
Brown ground beef in a large skillet over medium heat, drain fat and return to the pan.
Add ½ cup water, taco seasoning, onion, and peppers to the pan and cook until the water is absorbed and vegetables are tender.
Mix the Bisquick and 1 cup of water together and press into the bottom of the casserole dish and up the sides of the dish.
Spread the ground beef mixture over the Bisquick layer and top with the can of Rotel tomatoes and green chilies. Spread the sour cream mixture on top and sprinkle the remaining cheese on the very top.
Bake for 30-35 minutes or until it is heated through and cheese is melted.
Notes
Preheat oven and prep all ingredients for quick and easy assembly.
Rest casserole for 5 minutes after baking to help firm it up slightly before serving.
Refrigerate casserole up to 4 days and reheat in the oven covered with foil.
Freeze cooled portions in airtight containers for up to 6 weeks.