Cut polenta into 8 to 12 slices. Prepare polenta according to package directions. Cover and keep warm.
For ratatouille, in a 4-quart saucepan cook sweet pepper, onion, and garlic in hot oil over medium heat for 5 minutes, stirring frequently. Add the eggplant; cook for 5 minutes more, stirring frequently. Stir in summer squash or zucchini, tomato, pattypan squash, basil, salt, and pepper. Cook, covered, 5 to 7 minutes more or until vegetables are tender, stirring occasionally. Stir in parsley.
To serve, place 2 slices of polenta on each of 4 to 6 dinner plates. Spoon warm ratatouille over each serving. If desired, sprinkle with Parmesan cheese. Makes 4 to 6 servings.