Preheat the oven to 350 degrees Fahrenheit and lightly spray a large (13” x 9”) casserole dish with cooking oil.
Heat the avocado oil in a large skillet over medium heat and add the onion. Sauté, stirring frequently, until onion is translucent, about 4 to 6 minutes.
Add the ground beef and use a spatula to break it into smaller pieces to brown. If you'd like, drain the excess fat. Stir in the bell pepper, chili powder, garlic and diced green chilis, salt, black pepper, and continue cooking until everything is fragrant, about 3 minutes.
Transfer the thawed hash browns to the casserole dish in an even layer, followed by the ground beef mixture, sea salt, and half of the grated cheese. Stir everything until well-combined.
Whisk the eggs in a large bowl until well-beaten. Season with sea salt, then pour the egg mixture over the meat and potatoes evenly.
Top with the remaining grated cheese.
Bake on the center rack of the preheated oven for 45 to 55 minutes, or until the casserole has set up.
Allow the casserole to cool for 15 minutes before slicing and serving.
Serve breakfast taco casserole with your choice of toppings, such as sour cream, avocado slices, guacamole, diced tomatoes, spicy or mild salsa, hot sauce, etc.