Preheat oven to 425F. Combine zucchini, squash, onions, bell pepper & mushrooms in a mixing bowl. Add oil to the bowl. Toss veggies until they are coated lightly and evenly with the oil.
Combine seasoning with salt and pepper and sprinkle evenly over the vegetables. Toss he again to combine and spread them on a baking sheet. Place veggies in a hot oven and roast 20 to 25 minutes until tender. Toss and turn the veggies with kitchen tongs 1/2 way through cooking time.