Mash the avocado in a medium bowl. Add the salsa and mix.
Place bread slices on a clean work surface. Spread the avocado mixture over four slices of bread (reserve remaining avocado spread to serve on the side with the sandwiches). Top each with tomato slices, bacon and cheese. Finish with another slice of bread. Butter or oil each outer side of bread.
Saute sandwiches over medium heat until golden brown on both sides and the cheese is melted (a Panini maker can also be used). Cut sandwiches in half and serve.