Remove the stem from the mushrooms, and hollow out the cap. Reserve the mushroom stems, and cut off the woody end & discard. Dice up the remaining part of the mushroom stem & set aside along with the onion & garlic.
Fry the bacon in a pan until crispy. Remove the bacon to a paper towel, and reserve the grease.
Saute the diced mushroom stems, onion, & garlic for 5-7 minutes. Season with salt & pepper. Turn off the heat and add the cream cheese. Stir until melted & combined. Mix in the cheddar cheese & bacon.
Spoon the filling into the hollowed out mushroom caps. Pack the filling in, and pile any extra on top of the mushrooms. Sprinkle with paprika.
Bake in an oven preheated to 350 degrees for 20 minutes.