Fry bacon until crisp; drain well and cool. Combine the mayonnaise and butter. Stir in the cheese, onion, cayenne pepper until smooth. Spread mixture on baguette slices. Place on non-stick baking sheet. Bake at 350 degrees for 10 - 15 minutes or until cheese is melted and golden brown.
While the bread is baking - combine the chopped tomatoes with basil, vinegar, salt and pepper to taste.
When bread comes out of the oven, top with tomatoes and serve.