Place tomatoes in a colander; sprinkle with salt. Toss well. Drain in sink for 30 minutes.
Melt butter in a large saucepan over medium-high heat. Add onion; sauté 4 minutes or until browned. Add garlic; sauté 30 seconds. Add drained tomatoes, basil, chili powder, black pepper, and ground red pepper; bring to a boil. Reduce heat, and simmer 15 minutes. Stir in chopped zucchini and bell peppers; simmer 5 minutes or until peppers are crisp-tender.