Preheat oven to 350°F (175°C).
In a skillet, cook ground beef until browned. Drain excess fat.
Add taco seasoning to the beef and cook according to package instructions.
In a mixing bowl, combine sour cream, mayonnaise, and half of the shredded cheese.
In a baking dish, layer the Bisquick mix prepared with water, beef mixture, sour cream mixture, onions, bell peppers, and tomatoes.
Top with the remaining shredded cheese.
Bake for 30-35 minutes, or until the cheese is melted and bubbly.
Let it cool for a few minutes before serving.