Heat oven to 200 degrees with the oven rack adjusted to the middle.
PREPARE THE CHICKEN BREASTS
Cut the chicken breasts in half horizontally. Cover the chicken in wax paper or plastic wrap pound to an even 1/4 inch thickness with a meat pounder or bottom of a heavy, flat surface. You'll have 4 pieces.
Pat the chicken dry with a paper towel and season each slice with the salt and pepper.
Place the flour on a pie plate or regular large plate, and dip each chicken breast in flour, shaking off any excess, then transfer each piece to a separate plate.
Heat 3 tablespoons oil in a 12 inch non-stick skillet over medium heatPlace two chicken pieces in the skillet and cook until golden brown on one side, about 3 minutes. Turn chicken over and continue cooking for 3 more minutes, until the chicken is no longer pink inside. Wipe out skillet, and repeat with remaining oil and the other two pieces of chicken.
Place all chicken on a heatproof platter or shallow pie plate tented loosely with aluminum foil to keep them warm in the oven while you make the sauce.
Place the 1/2" pieces of bacon in the now empty skillet on medium heat, and cook until crisp, stirring and scraping the pan bits with a wooden spoon until the bacon is crisp, about 5 minutes. Remove bacon and transfer to a paper-towel lined plate.
COOK THE SHALLOTS
Place the two tablespoons of shallot in the now empty pan, and cook until soft, stirring occasionally with a wooden spoon, about 5 minutes.
MAKE THE MUSHROOM MARSALA WINE SAUCE
Add the sliced mushrooms to the pan with the shallot, and cook in the skillet on medium heat, stirring occasionally with a wooden spoon, until mushrooms are soften and lightly browned on the edges, 6-8 minutes.
Stir in the minced garlic clove, tomato paste and the cooked bacon, continue cooking for one minute, remove pan from heat.
Stir in the Marsala wine, a scrape up any bits from the bottom of the pan with your wooden spoon.
Return to the heat, increase to medium high, and cook the mixture for about 5 minutes, or until the sauce is slightly thickened, stirring it occasionally.
Turn off heat and stir in lemon juice and butter, another pinch of salt and pepper, and one tablespoon of the fresh parsley. Stir gently to combine together.
Remove chicken from the oven and place on a serving platter, pour warm sauce over the chicken and sprinkle with remaining fresh parsley and serve immediately.