Prepare the pasta according to package directions.
In a large saucepan with steamer basket, bring 1" of water to a boil. Steam the broccoli, mushrooms, zucchini, and yellow squash in the basket for 5 minutes, or until tender. (The time depends on the individual vegetables. The mushrooms will be tender before the squash, for instance.) Transfer to a colander to drain. Set aside.
In a large skillet over medium heat, heat the oil. Cook the tomato and garlic (if desired), stirring frequently, for 1 minute. Add the steamed vegetables, season with salt and pepper to taste and cook for 1 minute. Place the pasta in a serving bowl and top with the vegetable mixture.