• Preheat the oven to 375°F (190°C) and coat a 9x13-inch baking pan lightly with cooking spray or butter.

Prepare the biscuit crust:

• In a mixing bowl, combine the flour, baking powder, and salt. Incorporate the cold butter pieces into the dry mix using a pastry cutter or your fingers until a crumb-like texture forms. Gradually pour in the cold milk, stirring just until a soft dough takes shape. Gently press this dough into the base of the prepared dish to form an even layer.

Cook the meat and vegetables:

• In a large skillet set over medium heat, brown the ground beef until fully cooked. Stir in the diced onion and bell pepper, cooking for approximately 5 minutes until the vegetables soften. Sprinkle in the taco seasoning and pour in the water. Simmer the mixture for 2–3 minutes, allowing it to thicken. Fold in the drained diced tomatoes with green chilies and remove from heat.

Prepare the creamy cheese layer:

• In a separate bowl, whisk together the sour cream, mayonnaise, one cup of shredded cheddar cheese, black pepper, and garlic powder until smooth and evenly blended.

Assemble the dish:

• Distribute the seasoned beef mixture across the biscuit base. Spoon the cheese and sour cream blend over the meat and gently smooth it to cover. Sprinkle the remaining cheddar cheese across the top and finish by arranging the sliced tomato over the cheese layer.

Bake:

• Transfer the dish to the oven and bake for 35 to 40 minutes, or until the top is golden and bubbling.

Serve:

• Remove from oven and allow the casserole to rest for 5 minutes before cutting into portions. Serve warm.