TRIM EXCESS SKIN from the breasts. Sprinkle breasts with salt and pepper and set aside. Quarter larger mushrooms, halve smaller ones and set aside. Heat 1 tablespoon oil in an aluminum skillet or frying pan over high heat and brown chicken on skin side. Transfer the chicken to a plate and pour off fat. Reduce heat to medium, pour in vinegar and dissolve the tomato paste in it. Replace chicken in skillet, skin side up. Cover and cook 3 minutes. Uncover; cook until chicken is done, 6 minutes. While the chicken is cooking, heat 1 teaspoon oil in another frying pan and cook the mushrooms about 3-to-4 minutes. Arrange chicken and mushrooms on platter. Whisk in the rest of the olive oil; mix in parsley. Pour juices that have collected on the platter into sauce. Pour sauce over chicken and mushrooms; serve immediately.