In a large nonstick pan, cook sausage onion, and red pepper until sausage is no longer pink, breaking it apart with a wooden spoon as it cooks. Drain fat.
Spray a slow cooker with cooking spray or use a crock pot liner. Layer half the hash browns in the bottom of the slow cooker. Season with salt and pepper. Top with half the sausage mixture.
Sprinkle half the cheese and half the green onions on top of the sausage.
Spread remaining hash browns on top of cheese and season with salt and pepper. Spread the remaining sausage mixture on top of hash browns.
In a medium bowl, whisk together eggs, half-and-half, garlic salt, salt, and pepper.
Pour over casserole. Place lid on slow cooker and cook on LOW for 6 1/2 to 8 hours or until eggs are set.
Top with remaining cheese and green onion. Let sit until cheese melts.
Notes
If your crock pot runs hot, don't cook for longer than 7 hours or it will be dry.