Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.

Combine the Cheddar Bay biscuit mix, 1/2 cup shredded cheddar, and 3/4 cup milk in a large bowl until a soft dough forms. Keep the garlic-herb packet to one side for later.

Press the biscuit dough evenly into the bottom of the prepared baking dish to form the base.

Heat a skillet over medium-high heat and cook the ground beef, breaking it up with a spoon. Add the diced onion and red bell pepper and continue cooking until the meat is browned and the vegetables are softened.

Drain off any excess fat, then stir in the taco seasoning and 1/4 cup water. Reduce the heat and simmer briefly until most of the liquid evaporates and the mixture is well combined.

Spread the seasoned beef mixture evenly over the biscuit base in the baking dish.

In a medium bowl whisk together the sour cream, mayonnaise, 1 cup shredded cheddar, drained green chiles, and the reserved garlic-herb packet until smooth.

Carefully spread the creamy chile-cheese mixture over the beef layer, covering it evenly.

Sprinkle the remaining 1–2 cups shredded cheddar over the top, then bake in the preheated oven for about 30 minutes, or until the casserole is bubbly and the cheese is melted and lightly browned.

Remove from the oven and let the casserole rest for about 5 minutes before slicing and serving.