Place 1 oven rack in bottom rack position. Heat oven to 475°F. Spread tomatoes, bell peppers and onions in ungreased 15x10x1-inch baking pan. Drizzle with oil; toss to coat. Sprinkle with taco seasoning; toss to evenly coat. Bake at 475°F. on bottom oven rack for 15 minutes or until bell peppers and onions are crisp-tender.