Brown the sausage: Cook the turkey sausage and onion in a skillet over medium heat until the sausage is no longer pink. Drain any fat and set aside.
Whisk the eggs: In a large mixing bowl, whisk together the eggs, milk, taco seasoning, and shredded cheese.
Prepare the slow cooker: Spray the inside of your slow cooker with non-stick cooking spray.
Layer the ingredients: Add the frozen hash browns to the bottom of the slow cooker. Top with the cooked sausage mixture, diced bell peppers, and optional cilantro.
Pour the egg mixture: Evenly pour the egg mixture over the layered ingredients.
Cook to perfection: Cover and cook on high for 2 1/2 hours or low for 4-4 1/2 hours, or until the eggs are set. You’ll know it’s ready when the eggs are firm and not runny in the center.
Serve and garnish: Garnish with sliced green onion, and serve with salsa and sour cream if desired.