Wash mushrooms in cold water. Remove and discard stems. Place mushrooms in a shallow baking dish.
Add cream cheese, parmesan cheese, and garlic to a small skillet and heat over medium heat, stirring often, until mixture is creamy.
Using two spoons, (one to stuff, one to get the mixture off the spoon) stuff the mushrooms with the mixture.
Heat the grill, and lay a sheet of aluminum foil onto the grill grate, and cook the mushrooms until they are a nice golden color. This takes about 15-20 minutes on a gas grill heated at medium/low.
Serve hot.
Notes
*Cooking time may be different for charcoal grills.