Preheat the oven to 350°F with the rack in the center. Grease a 13×9 baking dish.
Place the biscuits in a single layer and press them together, pushing the dough halfway up the sides of the pan. Set the dish on a baking sheet and bake for 12 to 15 minutes, checking after 12, until the dough is very lightly browned at the edges. Remove and set aside, leaving the oven on.
While the biscuits bake, combine the browned ground beef with the taco seasoning and water, and cook according to the packet instructions. Transfer to a bowl and set aside, then wipe out the pan.
In a separate bowl, combine the sour cream, mayonnaise, half of the cheddar, and half of the onions. Stir well and set aside.
In the same pan used for the beef, sauté the remaining onions and the bell pepper until slightly tender.
On top of the baked biscuit crust, layer in this order: taco meat, tomato slices, the pepper and onion mixture, jalapeños, the sour cream mixture, and the remaining cheese. Bake uncovered for 30 to 40 minutes, until the edges of the dough are lightly browned and the cheese is melted.