Preheat oven to 425°F. Toss diced zucchini, bell pepper, and red onion with olive oil, salt, pepper, and cumin. Spread on a baking sheet and roast for 20–25 minutes, flipping halfway.
1 zucchini, 1 red bell pepper, 1 red onion, 1 tbsp olive oil, 1 tsp cumin, 1 tsp salt, 1/2 tsp black pepper