01 - Preheat oven to 350°F, positioning a rack in the middle position.
02 - Heat 1 tablespoon olive oil in a 9-inch oven-safe nonstick skillet over medium heat. Add diced pancetta and cook for 3-4 minutes, stirring occasionally, until crisp and rendered. Remove pancetta with a slotted spoon and set aside, leaving the rendered fat in the pan.
03 - Add remaining 1 tablespoon olive oil to the skillet along with sliced zucchini and chopped onion. Sauté for 5-6 minutes until vegetables are tender and lightly golden.
04 - In a large mixing bowl, whisk together eggs, milk, grated Parmesan, chopped fresh herbs, salt, and black pepper until well combined.
05 - Stir cooked pancetta into the zucchini-onion mixture. Pour the egg mixture evenly over the vegetables and pancetta in the skillet.
06 - Cook on the stovetop over medium heat for 2-3 minutes until the edges begin to set and pull away from the pan sides.
07 - Transfer the skillet to the preheated oven. Bake for 10-12 minutes, or until the frittata is puffed, golden on top, and just set in the center when gently shaken.
08 - Let the frittata cool for a few minutes before slicing into wedges. Serve warm or at room temperature.