Rinse, pat dry and chop mushrooms. Set aside. Cook spinach, covered, only with the water clinging to the leaves until barely wilted. Drain well, squeezing out excess water. Chop (should make about 1/2 cup). Set aside. In a large skillet, heat 2 Tbsp. of the oil until hot. Add onions and mushrooms. Sauté until tender, about 4 minutes. Add garlic, oregano, pepper, salt and spinach. Cook and stir well for 1 minute. Set aside to cool.

Meanwhile, flatten each chicken breast, place them between 2 sheets of wax paper or plastic wrap and pound them with a mallet until about 1/4 inch thick. Spoon 1/4 of the mushroom/spinach mixture onto the center of each chicken breast. Roll lengthwise. Secure with toothpicks.

Place rolled chicken breasts into a 9 inch square pan. Combine chicken broth with remaining 2 Tbsp. of oil. Spoon over chicken. Bake uncovered, basting frequently, until chicken is tender, about 15 - 20 minutes. Sprinkle with chopped parsley before serving (optional).

Note: You can make the mushroom/spinach mixture the night before and refrigerate it. Let it come to room temperature before using. You can also use the spinach filling to stuff chicken bottoms, just lift up the skin and push the spinach mixture inside.