In large saute pan over medium-high heat, melt butter. Stir in onion, celery and bell peppers. Saute vegetables until onions are translucent (about 5 minutes). Reduce heat to medium. Stir in mushrooms and tomatoes; cook, covered, for 15 minutes. Stir in eggplant, zucchini, garlic, salt and cayenne pepper. Simmer, covered, 20 minutes, stirring occasionally. Remove from heat; stir in basil.