Preheat your oven to 350°F (175°C).
Line the baking sheet with parchment paper for easy clean-up.
In a mixing bowl, whisk together the eggs and milk until well combined.
Add the salt, black pepper, and garlic powder to the egg mixture and stir until evenly distributed.
Spread the diced bell peppers, chopped spinach, and halved cherry tomatoes evenly across the baking sheet.
Pour the egg mixture over the vegetables, ensuring they are all submerged.
Sprinkle the shredded cheese evenly across the top of the egg mixture.
Bake in the preheated oven for 20 minutes, or until the eggs are set and slightly golden on top.
Remove from the oven and let it cool for a few minutes. Cut into squares or rectangles for serving.
Serve warm, garnished with fresh herbs if desired.