Preheat oven to 375°F (190°C) and grease a 9x13-inch ceramic baking dish with cooking spray or butter.

In a large skillet over medium-high heat, warm olive oil. Add the turkey sausage, breaking it into bite-sized crumbles with a wooden spoon for 5 to 6 minutes until browned and cooked through. Add diced onions and bell peppers, sautéing for 3 more minutes until tender. Remove from heat and drain any excess liquid.

Spread thawed shredded hashbrowns evenly across the bottom of the prepared baking dish. Scatter the browned sausage, onions, bell peppers, and 2 cups of the combined cheeses over the potatoes, tossing gently to distribute evenly.

In a large bowl, whisk together the eggs, milk, sour cream, garlic powder, onion powder, smoked paprika, salt, and black pepper until completely smooth and aerated.

Pour the egg mixture evenly over the hashbrowns and sausage, pressing down lightly with a spatula to ensure the potatoes absorb the custard. Top with the remaining 1 cup of shredded cheddar.

Bake uncovered at 375°F for 40 to 45 minutes, until the center is set (a knife inserted comes out clean) and the cheese on top is melted, bubbly, and golden-brown.

Remove from the oven and let rest for 10 minutes to allow the layers to settle cleanly before slicing into squares. Garnish with sliced green onions and serve warm.