01 - Preheat oven to 350°F. Lightly grease a 9-inch pie dish with olive oil.
02 - Scatter the halved cherry tomatoes, chopped spinach, and diced red onion evenly across the bottom of the prepared pie dish.
03 - Sprinkle the shredded mozzarella and grated Parmesan evenly over the vegetable layer.
04 - In a large mixing bowl, whisk together the eggs, whole milk, olive oil, dried Italian herbs, garlic powder, salt, and black pepper until well combined.
05 - Gradually add the all-purpose flour to the egg mixture, whisking steadily until the batter is smooth and free of lumps.
06 - Pour the batter evenly over the vegetables and cheese in the pie dish, allowing it to settle into the layers.
07 - Bake on the center rack for 40 minutes, or until the top is golden brown, puffed, and the center is set when gently shaken.
08 - Remove from the oven and let rest for 5 to 10 minutes before slicing into wedges. Serve warm or at room temperature.