Preheat the oven to 350°F.
Spray a 18x13-inch rimmed baking sheet with nonstick cooking spray and line with parchment paper.
In a large bowl, whisk together eggs, milk, salt, pepper, garlic powder, onion powder, and dried parsley until well combined.
Pour the egg mixture onto the prepared sheet pan. Evenly sprinkle the diced bell pepper, diced onion, chopped spinach, and shredded cheddar cheese over the top.
Bake in the preheated oven for 15-20 minutes, or until the eggs are set and no longer jiggly in the center.
Allow the eggs to cool slightly, then cut into 12 equal pieces. Serve warm with preferred toppings.