01 - Heat olive oil in an ovenproof skillet over medium heat. Add onion, red bell pepper, zucchini, and kale; sauté until softened, about 5 minutes.
02 - In a large bowl, whisk together eggs, heavy cream, Parmesan cheese, salt, and black pepper until smooth.
03 - Pour the egg mixture over the sautéed vegetables in the skillet, stirring gently to combine. Cook undisturbed over medium-low heat until edges begin to set, approximately 5 minutes.
04 - Transfer the skillet to a preheated 350°F oven and bake for 12 minutes or until the frittata is fully set and lightly golden on top.
05 - Remove from oven, let rest briefly, then slice and serve warm.