Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish with nonstick spray.

In a large skillet over medium-high heat, brown the breakfast sausage, breaking it up into crumbles as it cooks. Drain any excess grease.

Spread the thawed hashbrowns in an even layer across the bottom of the prepared baking dish.

Sprinkle the cooked sausage, diced bell pepper, diced onion, and 1 ½ cups of the cheddar cheese evenly over the hashbrowns.

In a large bowl, whisk together the eggs, milk, salt, and pepper until completely smooth and frothy.

Pour the egg mixture evenly over the hashbrown and sausage layers in the baking dish.

Bake uncovered for 40-45 minutes, or until the edges are golden brown and a knife inserted into the center comes out clean.

Sprinkle the remaining ½ cup of cheddar cheese over the top and bake for an additional 5 minutes until melted and bubbly.

Let the casserole rest for 10 minutes before slicing. Garnish with fresh chives and serve hot!