Preheat the oven to 350°F and adjust the rack to the center position. Lightly grease a 13×9-inch glass baking dish.

Arrange biscuits in a single layer in the prepared dish, pressing them together and up the sides halfway. Set the dish on a baking sheet and bake for 12–15 minutes, watching closely after 12 minutes. The edges should be barely golden. Remove and keep the oven on.

While the biscuits bake, cook the ground beef with the taco seasoning and specified amount of water according to package instructions. Set the seasoned beef aside.

In a clean bowl, stir together the sour cream, mayonnaise, 4 ounces of cheddar cheese, and half of the sliced onion. Mix until smooth and set aside.

Using the same skillet, sauté the remaining onion and red bell pepper until slightly softened.

To assemble, layer the following over the baked biscuit base: seasoned beef, tomato slices, sautéed peppers and onions, jalapeño slices, then spread the sour cream mixture evenly on top. Finish with the remaining 4 ounces of shredded cheese.

Bake the assembled casserole uncovered for 30–40 minutes, until the cheese is melted and the biscuit crust is lightly golden around the edges.