Prep the oven and pan: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with olive oil or cooking spray.

Pre-crisp the hashbrowns: Toss thawed hashbrowns with 1 tablespoon oil, a pinch of salt, and pepper. Spread in the dish and bake for 15 minutes to dry and lightly crisp. This keeps the final casserole from getting soggy.

Cook the sausage: While the hashbrowns bake, warm a skillet over medium heat. Add sausage and cook until browned. Remove and set aside.

Sauté the veggies: In the same skillet, add the remaining 1 tablespoon oil. Sauté onion and bell pepper with a pinch of salt for 4–5 minutes until softened. Add garlic and cook 30 seconds. Stir in spinach until just wilted. Remove from heat.

Whisk the egg mixture: In a large bowl, whisk eggs, egg whites, Greek yogurt, and milk until smooth. Add smoked paprika, 1 teaspoon salt, and black pepper. Stir in half the cheese.

Assemble: Scatter the cooked sausage and sautéed vegetables evenly over the par-baked hashbrowns. Pour the egg mixture over the top. Sprinkle with the remaining cheese.

Bake: Return the dish to the oven and bake for 28–35 minutes, until the center is set and a knife inserted in the middle comes out mostly clean. If the top browns too quickly, tent loosely with foil.

Rest and serve: Let the casserole rest for 10 minutes to set. Slice and serve with green onions, hot sauce, salsa, or avocado if you like.