Preheat oven to 400°F (200°C).
In a mixing bowl, toss bell peppers, zucchini, and cherry tomatoes with olive oil, salt, and black pepper.
Spread the vegetables on a baking sheet and roast for 25-30 minutes, until tender and slightly charred.
While the vegetables are roasting, bring water and salt to a boil in a pot. Gradually whisk in the polenta.
Reduce heat to low and cook, stirring frequently, until the polenta thickens, about 15 minutes.
Stir in butter and Parmesan cheese until melted and well combined.
Spread the cooked polenta on a baking sheet and broil for 5 minutes until the top is golden and crispy.
Serve the roasted vegetables over the broiled polenta.