Line large plate with paper towels and set aside.
Place large skillet on stovetop over medium heat. When skillet is warm, add 1 pound diced bacon. Cook bacon, stirring occasionally, until crisp.
Transfer cooked bacon to plate lined with paper towels and set aside. Discard rendered bacon fat, or save bacon fat for other uses (like bacon gravy). Crack 12 large eggs directly into large mixing bowl. Add 2 cups half and half, 1 teaspoon garlic powder, 1 ½ teaspoons salt, and ½ teaspoon freshly ground black pepper. Whisk ingredients together until mixture is fully combined and eggs are no longer streaky.
Add 2 ½ cups shredded cheese of choice, 1 26-ounce bag frozen shredded hashbrowns, and 1 cup chopped onion to mixing bowl with scrambled egg mixture. Break cooked bacon into small pieces and add to scrambled egg mixture. Stir ingredients together until fully incorporated.
Spray bottom and sides of Crockpot insert with neutral spray oil. Transfer scrambled egg mixture to prepared Crockpot insert and cover with lid.
Cook casserole on LOW 8 hours.
After 7 ½ hours, check doneness of casserole to ensure eggs are fully cooked. Continue cooking as needed, checking casserole often until eggs are fully cooked. Do not exceed 8 ½ hours total.
Once eggs are fully cooked, sprinkle ½ cup shredded cheese of choice evenly across surface of casserole. Cover and cook on LOW 30 minutes or until cheese is completely melted.
When cheese is melted, garnish casserole with diced, cooked bacon and chopped green onions if desired and serve warm with salsa or condiments of choice. Alternately, switch Crockpot to WARM setting until ready to serve. Garnish before serving if desired.