In a medium pan, sautè mushrooms and garlic. Season with salt and pepper. Add olive oil to the pan once the mushrooms have released any liquid and they start to look a little dry. Continue to sautè for a few minutes. Remove from heat.
Using some of the oil from the mushrooms, brush oil on the bottom of two slices of bread. Add tomatoes to each slice and season with salt. Add some basil leaves and the mushroom mixture. Top each with another piece of bread and brush more oil on the top of the sandwiches.
Put in a panini press and toast until golden brown.