1. Sauté bacon in a large skillet over medium-high heat 8 minutes or until crisp; remove bacon, and drain on paper towels, reserving 2 Tbsp. drippings in skillet.
2. Sauté onion and next 4 ingredients in hot drippings 4 minutes or until onion is tender. Add zucchini and yellow squash; cook, stirring often, 10 minutes. Stir in tomatoes, and cook, stirring occasionally, 10 minutes. Remove from heat, and stir in butter and vinegar. Season with salt and pepper to taste. Garnish, if desired.