Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish.

In a large bowl, whisk together 2 cups all-purpose flour, 2 teaspoons baking powder, and 1/2 teaspoon salt. Cut in 1/2 cup cold, cubed unsalted butter until the mixture resembles coarse crumbs. Stir in 3/4 cup whole milk until a soft dough forms, then press it evenly into the bottom of the prepared baking dish.

In a large skillet over medium heat, brown 1 pound ground beef, breaking it up as it cooks. Once the meat is cooked through, add 1 diced medium yellow onion and 1 diced green bell pepper, cooking until they have softened, about 5 minutes.

Stir in 1 packet of taco seasoning and 1/2 cup water, then allow the mixture to simmer for 2-3 minutes until slightly thickened. Spoon this seasoned beef mixture over the crust in the baking dish, then top evenly with the drained can of diced tomatoes with green chilies.

In a separate bowl, mix together 1/2 cup sour cream, 1/2 cup mayonnaise, 1/2 teaspoon black pepper, and 1/2 teaspoon garlic powder until smooth. Fold in 1 cup of shredded cheddar cheese. Spread the creamy mixture over the beef layer.

Arrange the sliced small tomato on top, then sprinkle the remaining 1 cup of shredded cheddar cheese over the casserole.

Bake the casserole for about 30-35 minutes until the cheese is melted, bubbly, and the crust is golden brown. Allow it to rest for 5-10 minutes before slicing and serving.