Preheat the oven to 350°F (180°C) and lightly grease a 9x13-inch baking dish with cooking spray.
Cooking spray
In a medium bowl, stir together the baking mix, milk, and oil. Spread the mixture evenly in the prepared dish and bake for 10 to 15 minutes, or until it starts to turn golden brown. Remove from the oven and set aside.
1 ¼ cups whole milk, 2 cups all-purpose baking mix
Heat 1 tablespoon of oil in a large skillet over medium-high heat. Add the ground beef and cook, stirring occasionally, until almost cooked through with a bit of pink remaining, about 5 minutes. Add the onion and pepper, and cook, stirring occasionally and breaking the beef into small pieces, until the beef is fully cooked and the onions soften, about 3 minutes. Stir in the taco seasoning and salt, and remove from heat. Set aside.
2 tablespoons vegetable oil, 2 pounds ground beef, ½ small yellow onion, ¾ cup red bell pepper, 2 tablespoons taco seasoning mix, ¾ teaspoon kosher salt
In a medium bowl, mix together the mayonnaise, sour cream, and 1 cup each of pepper jack and cheddar cheese. Set aside.
½ cup mayonnaise, 2 cups shredded cheese mix, ½ cup sour cream
Spoon the beef mixture evenly over the par-baked biscuit in the baking dish. Top with the drained diced tomatoes and green chiles, followed by the mayonnaise mixture. Gently spread to cover, then sprinkle with the remaining cheese.
2 cups diced tomatoes and green chiles
Bake for about 30 minutes, or until the casserole is bubbly and the cheese is melted and starting to brown. Remove from the oven and let it rest for 10 minutes before serving.