Sautee the onion and broccoli in one tablespoon of the olive oil over medium heat in an 8-inch cast iron pan until both have softened, about 5 minutes.
Mix beaten eggs with herbs, garlic powder, salt and pepper.
Flatten the vegetables along the bottom of the pan. Drizzle one tablespoon olive oil over the vegetables.
Slowly pour the egg mixture evenly over the vegetables. The vegetables will be mostly covered by the eggs.
Arrange the cherry tomato halves evenly around the frittata.
Cover the frittata with the parmesan cheese.
Preheat the oven to broil.
Cook the frittata on the stove until the edges and bottom are cooked (but not browned), and the top is still a little runny.
Put the pan under the broiler and watch carefully as the top of the frittata finishes cooking and begins to brown (2-3 minutes). Don’t overcook.
Remove from the oven and let cool.
Use a spatula to loosen from the pan. Serve warm or room temperature.