Saut 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.
Saut 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.