Heat oven to 400 degrees F. Lightly oil two baking sheets. Cut zucchini and summer squash lengthwise in half, then cut each half crosswise into large chunks (about 1 1/2-inch thick). In medium bowl, toss zucchini and squash with chopped pecans, 2 teaspoons olive oil, and 1/4 teaspoon salt. Spread mixture in a single layer on one baking sheet. Set aside.
Cut red onion into 1-inch thick wedges and place in same bowl. Cut tomatoes lengthwise into quarters and add to onion. Toss onion and tomatoes with remaining 2 teaspoons oil and 1/4 teaspoon salt. Spread mixture in a single layer on second baking sheet.
Roast all vegetables 5 minutes. Turn vegetables and pecans and roast 4 – 5 minutes longer or until most of the vegetables are just tender and lightly browned-do not overcook. Combine all the vegetables and chopped pecans in a large bowl, sprinkle with vinegar and gently stir.
To serve, divide salad greens among plates. Top each with a mixture of vegetables and chopped pecans. Pour any liquid in bowl over vegetables. Garnish each serving with 3 pecan halves and, if desired, Parmesan cheese.
Nutrition information per serving (without Parmesan)-237 calories; 5g protein; 17g carbohydrates; 5g fiber; 17g fat; 1g saturated fat; 0 cholesterol; 291mg sodium.