Preheat your oven to 375°F (190°C). Make sure the oven reaches the correct temperature before baking. This helps the frittata cook evenly and develop a nice texture.

Wash all vegetables carefully. Chop the spinach, onion, bell pepper, and zucchini into small pieces. Small pieces cook faster and spread evenly throughout the frittata.

Heat olive oil in an oven-safe skillet over medium heat. Add onion, zucchini, and bell pepper. Cook for about five minutes until slightly soft and fragrant.

Add chopped spinach to the skillet. Stir gently for one to two minutes. The spinach will soften quickly and blend well with the other vegetables.

In a large bowl, crack the eggs. Add milk, salt, and black pepper. Whisk everything together until the mixture becomes smooth, light, and slightly frothy.

Pour the egg mixture over the vegetables in the skillet. Sprinkle the shredded cheese and chopped parsley evenly across the top for extra flavor.

Let the frittata cook for three to four minutes without stirring. The edges should begin to set while the center remains slightly soft.

Transfer the skillet carefully to the oven. Bake for about 20 minutes until the center is fully set and the top becomes lightly golden.

Remove the skillet from the oven. Allow the frittata to cool for five minutes. This helps it firm up and makes slicing easier.

Slice into six portions and serve warm. Enjoy a healthy meal packed with vegetables, protein, and delicious homemade flavor.