Heat a large skillet over medium heat. If using Bacon (3 slice), add to skillet and cook until crisp and fat has rendered. Scoop out the bacon to a paper towel-lined plate. Remove all but a tablespoon of fat. If not using bacon, simply heat a tablespoon of olive oil in a large skillet over medium heat.
Add Shallot (1) and Garlic (2 clove) and sauté, stirring often until starting to soften about 3 minutes.
Add Mushroom (10 ounce) and continue to cook until most of the moisture has cooked out about 8-10 minutes.
Add White Wine (1/4 cup), Fresh Thyme (1 teaspoon), Salt (1/4 teaspoon) and Ground Black Pepper (1/4 teaspoon) and cook until wine has cooked out, about 3 minutes.
Stir in Garden Vegetable Cream Cheese (1/2 cup), Gruyère Cheese (1/4 cup) and bacon, if using.
Preheat oven to 425 degrees F (218 degrees C) and lightly spray a 4 3/4 to 5 3/4x14-inch tart pan with removable bottom. (Basically, a long skinny rectangular pan).
Fit Puff Pastry (1 sheet) into tart pan and trim the top so it is level with the pan. You will need to cut the puff pastry sheet in two pieces to make it fit.
Spread filling evenly into pastry shell and sprinkle with remaining Gruyère Cheese (1/4 cup). Bake for about 25 minutes until golden and filling is bubbly.
Allow tart to rest for a couple of minutes prior to removing the outer pan. Cut into wedges, garnish with more fresh thyme and serve.