Prepare grill or broiler.
Sprinkle steaks with 1/4 teaspoon salt and 1/4 teaspoon pepper.
Combine 1/4 teaspoon salt, 1/4 teaspoon pepper, zucchini, and next 5 ingredients (zucchini through garlic) in a large zip-top plastic bag. Seal and shake to coat.
Place the tenderloin steaks on grill rack or broiler pan coated with cooking spray; cook for 4 minutes on each side or until desired degree of doneness. Place the zucchini and yellow squash on grill rack or broiler pan coated with cooking spray; cook 3 minutes on each side or until tender. Place the tomato and onions on grill rack or broiler pan; cook 2 minutes or just until tender.
Coarsely chop the vegetables, and place in a bowl. Add pesto; stir gently. Serve with steaks. Garnish with oregano, if desired.