Season chicken to taste with salt and pepper. Roll in breadcrumbs and sauté in 4 Tbls. butter in skillet until cooked through. Meanwhile, blanch spinach in boiling water for 1 minute. Drain. Brown half of remaining butter in another skillet and sauté spinach until just tender. Remove chicken from pan and add remaining butter. Add minced mushrooms and sauté until light brown. Place spinach on platter. Arrange chicken breasts over spinach and cover with mushrooms. Drizzle butter remaining in pan over chicken. Garnish with whole mushrooms.
For the whole mushrooms on top- toss the mushrooms in olive oil, minced garlic, and chopped fresh thyme and arrage on a roasting pan. Lightly season with salt and pepper and roast at about 400 degrees for just under 10 minutes or until they become nice and tender. Top the finished dish with the roasted mushrooms. Mushrooms can be made ahead of time and placed in fridge covered with clear wrap.