Preheat your oven to 350 degrees F and prepare a 9-inch pie dish with non-stick cooking spray.
In a skillet, heat olive oil over medium heat and sauté broccoli and red bell pepper until they begin to soften, about 5 minutes. Add green onions, garlic, salt, and pepper, and cook for another minute.
Whisk eggs in a large bowl, then fold in the cheddar cheese, shredded chicken, and sautéed vegetables.
Pour the egg mixture into the prepared pie dish and bake for 40 minutes, or until the frittata is set and a toothpick comes out clean.