PREPARATION:

1. Clean the mushrooms, then cut off the stems. Next, cut mushrooms into quarters and set aside in a bowl.  Peel the onion and slice in two, then cut each piece in half again. Afterward, chop up the onion.
2. Heat a medium-large frying pan on medium heat. Spritz olive oil on the bottom of the pan. Once the oil is warm (not hot, or the oil will evaporate), toss in the mushrooms and onions. Cook until marinated slightly together (not quite brown).
3. Clean the turkey, rinsing in cold water.  Take butter and rub it on your hands. Work the butter underneath the skin of the turkey.  Take half the lemon and squeeze lemon juice on the mushrooms, onions and turkey. 
4. Put the mushrooms and onions in the cavity of the turkey breast. Rub olive oil on the turkey. Cook turkey until juices run clear (no pink is left).
5. Once turkey is cooked, top with the mushroom and onions and any leftover sauce. Sprinkle with oregano.
6. To add flavor and increase tenderness, place some mushrooms and onions underneath the skin to marinate the juices into the turkey.