Colorful Ratatouille Baking Sauce

From today's Ft. Lauderdale Sun-Sentinel

1 tablespoon olive oil
1/2 large Spanish onion, diced into 1/2-inch cubes
1 large zucchini, diced into 1/2-inch cubes
2 small yellow squash, diced into 1/2-inch cubes
1 medium green bell pepper, cored, seeded, diced into 1/2-inch cubes
1/2 red bell pepper, cored, seeded, diced into 1/2-inch cubes
1/2 yellow bell pepper, cored, seeded, diced into 1/2-inch cubes
3 cloves minced garlic
2 teaspoons dried Italian seasoning
1/2 teaspoon crushed dried red chili flakes
2 (32-ounce) jars marinara sauce
1 cup shredded basil leaves

Heat oil over medium heat in a nonreactive large saucepan.

Add onions and sauté 1 minute to coat with oil. Add remaining vegetables, garlic, Italian seasoning and chili flakes and sauté 3 minutes to combine well. Add the marinara sauce, bring to a boil, reduce heat and simmer 20 minutes. Add basil and cool at room temperature. Makes 10 cups; serves 12.