Preheat your oven to 350°F (175°C).

In a large skillet over medium heat, add the lean ground beef and chopped yellow onion. Cook, stirring for about 5-7 minutes until browned and onion is translucent. Drain excess fat.

In a mixing bowl, combine the beef and onion mixture with diced red bell pepper, taco seasoning, and diced green chiles. Stir well.

In a separate bowl, combine the biscuit mix with water, sour cream, and mayonnaise. Mix until smooth.

Grease your baking dish, pour in half of the biscuit mixture as the base layer. Layer in the beef mixture, sprinkle with cheese, and finish with the remaining biscuit mixture.

Bake for 30-35 minutes until the top is golden brown and bubbly.

Remove the casserole and cool for about 10 minutes. Garnish with crispy fried onions and serve.