Heat the oven to 350°F (175°C). Grease a 9x13-inch baking dish.
Cook the meat: In a large skillet, brown the sausage over medium heat, breaking it up as it cooks, 6–8 minutes. If using bacon, cook until crisp.
Drain excess fat, leaving about 1 tablespoon for flavor.
Sauté the veggies: Add onion and bell pepper to the skillet with a little oil if needed. Cook until softened, 3–4 minutes. Stir in garlic for 30 seconds.
Add spinach and wilt, 1 minute. Season lightly with salt and pepper.
Prep the hash browns: Pat thawed hash browns dry with paper towels. Spread them in the greased dish.
Drizzle with a little oil or dot with butter. Sprinkle with a pinch of salt, pepper, and paprika.
Layer the flavor: Scatter the cooked sausage (or bacon) and sautéed veggies evenly over the hash browns. Sprinkle 1 cup of the shredded cheese over the top.
Whisk the eggs: In a large bowl, whisk eggs, milk, cottage cheese, 1/2 teaspoon salt, 1/2 teaspoon pepper, and paprika until smooth.
The cottage cheese should break up but doesn’t need to be fully pureed.
Combine and bake: Pour the egg mixture evenly over the layers. Top with the remaining 1/2 cup cheese. Bake 40–50 minutes, until the center is set and the top is golden.
A knife inserted in the center should come out clean.
Rest and serve: Let it rest 10 minutes so it slices cleanly. Garnish with chives or parsley. Serve warm.