Preheat your oven to 400°F.
Heat the olive oil in a large, oven-safe skillet over medium to medium-high heat.
Dice the zucchini and squash, then add them to the skillet. Sauté for 8–10 minutes, stirring occasionally, until softened.
Dice the shallots and stir them into the skillet with the zucchini mixture. Sauté for an additional 2–3 minutes.
Add the cauliflower rice, black beans, sweet corn, salt, pepper, and garlic powder. Stir until everything is well combined.
Mix in half of the shredded cheddar cheese, ensuring it’s evenly distributed. Pat the mixture into an even layer in the skillet.
Sprinkle the remaining cheese evenly over the top.
Transfer the skillet to the oven and bake for 10 minutes or until the cheese is melted and bubbly.
While the casserole bakes, chop the fresh parsley.
Remove the skillet from the oven and let it cool for a few minutes. Garnish with parsley and serve warm.