Heat oven to 375 degrees. Grease 13 x 9 x 2 baking dish. Cook beef until brown, drain. Mix sour cream, mayonnaise, cheese and onion. Mix bisquick and water, pat in pan pressing 1/2 inch up sides of baking dish. Layer beef, tomatoes and pepper. Spoon cheese mixture on top. Bake about 30 minutes. I have substituted 1/2 cottage cheese, 1/2 light sour cream instead of all sour cream has worked very well.