Preheat oven to 350 degrees F. Lightly spray a 9x13 inch baking dish with nonstick spray.

In a bowl combine Bisquick baking mix and 8 ounces of water and stir together until well mixed to make the biscuit dough.

Spread the biscuit dough over the bottom of the baking dish and pat it out so it covers the entire bottom of the dish. Set aside.

In a skillet over medium high heat add 1 tablespoon of olive oil and cook the onions and green peppers until they begin to soften.

Add the ground beef to the pan and cook until it is browned.

Remove the ground beef from the heat and drain off any excess grease. Then return the ground beef mixture to the skillet and add the taco seasoning and Rotel diced tomatoes with chilies (undrained). Stir together and continue to cook for 5 minutes.

While the ground beef finishes cooking, in a small bowl combine the sour cream, mayonnaise, and 4 ounces of cheddar cheese. Stir together.

Begin assembling the casserole by spooning the ground beef mixture over the biscuit dough in the baking dish.

Spread the sour cream mixture evenly over the ground beef layer.

Top with the remaining 4 ounces of cheddar cheese.

Bake for 40 - 45 minutes until the cheese is melted and bubbling on top.

Remove from oven and let rest for 10 minutes before serving.