In a frying pan heat butter over medium/high heat. Add mushrooms and saute (stirring frequently to prevent burning) until liquid evaporates (about 3-5 min.). Add shallots and garlic, saute for 1 more minute. Add flat-leaf parsley, salt and pepper to taste. Remove from heat.
Slice baguette on 1 inch diagonals.
Brush one side with olive oil. Place slices on a baking sheet(oil side up) and broil in oven until LIGHTLY golden brown (this happens quickly so don't walk away).
Remove from oven and spread each slice with basil pesto and topped with mushroom mixture. Last but not least sprinkle with cheese. Return to a preheated 375 degree F. oven. Bake until cheese is melted and center toppings are hot (about 2-5 minutes).