Preheat the oven to 400°F. In a large skillet, heat olive oil over medium-high heat. Add ground beef and cook until browned. Stir in the diced onion, garlic, celery, and green bell pepper.
Season with cumin, paprika, salt, and pepper. Add diced tomatoes and simmer for 15 minutes until thickened.
Spread 2/3 of the frozen hash browns evenly in a greased 9x13-inch baking dish.
Top with the beef and vegetables, then sprinkle 2 cups of shredded cheddar cheese. Add remaining hash browns loosely on top and sprinkle on salt and pepper.
Bake uncovered for 45 minutes. Sprinkle remaining cheese on the dish and return to the oven for another 15 minutes until melted.
Allow the casserole to cool for a few minutes before serving; garnish with green onions, if desired.