Preheat oven to 400 degrees. On a rimmed baking sheet, toss onion, bell pepper, and zucchini with oil and oregano. Bake 15 minutes.
Sprinkle vegetables with vinegar, and season with salt; toss to coat. Push vegetables to one side of pan; place meatballs on other end.
Bake until meatballs are cooked through and vegetables are tender, about 15 minutes. Serve in rolls.