Place broccoli in a steamer basket. Place in a saucepan over 1 in. of water. Bring to a boil; cover and steam for 5 minutes. Add zucchini and yellow pepper; cover and steam for 2 minutes or until vegetables are crisp-tender.
In a jar with a tight-fitting lid, combine the oil, vinegar, garlic, salt and thyme; shake well. Transfer vegetables to a serving bowl; add dressing and toss to coat.