Heat oven to 325. Brown ground beef and add taco seasoning and water, according to packet instructions; set aside.
In a separate bowl, combine sour cream, mayonnaise, 4 ounces of cheddar cheese, and half of the onions; set aside.
Stir biscuit mix and water (directions on box) to form soft dough. Pat dough on the bottom and one-half-inch up the sides of an 9 x 13 inches greased casserole dish.
Saute remaining onions and bell peppers until slightly tender.
On top of biscuit mix, evenly distribute ingredients in the following order: ground beef, tomato slices, green peppers, onions, jalapeno peppers, sour cream mixture and end with remaining shredded cheese.
Bake for 30-40 minutes or until edges of dough are lightly browned.