1 medium (10 to 12 ounces) Texas SpringSweet or 1015 Texas SuperSweet onion, thinly sliced and separated into rings
3 ripe tomatoes, sliced
1 cucumber, peeled and sliced
1/2 cup vegetable oil
1/4 cup white wine vinegar
1 tsp. Dijon mustard
1/2 tsp. salt
1/4 tsp. black pepper
1/4 tsp. sugar
1/4 cup sliced fresh basil leaves
Shaved fresh Parmesan cheese

Place half of the onion rings in a large, shallow casserole dish. Layer the tomato and cucumber slices over the onion and top with the remaining onion rings. In a small bowl, combine the oil, vinegar, mustard, salt, pepper and sugar; whisk well to blend. Pour over vegetables. Top with fresh basil. Cover and let marinate several hours in refrigerator. Top with cheese before serving.
Makes 8 to 10 servings.