Preheat oven to 325 degrees.
Dry the chicken.
Place an ovenproof skillet over moderate heat.
Add the oil to the skillet when it gets warm.
When the oil is hot, add half the onions to the pan and place the chicken in the pan with the onions.
Cook the chicken for about 8 minutes or until it will release itself easily from the pan, then flip to cook the other side.
Continue to cook for 4 minutes.
Stir the onions to keep from burning.
Remove the chicken from the skillet and set aside.
Place remaining onions and tomatoes over the caramelized onions in pan.
Allow the onions and tomatoes to sweat in the pan for 3-4 minutes.
Reduce heat and add wine to deglaze the pan.
With a spoon stir the pan to remove the browned bits from the bottom of the pan.
This deglazing technique will remove the flavor stuck to the bottom of the pan and release it to the vegetables.
Put the chicken back into the skillet.
Add stock just until the liquid level reaches halfway up the sides of the chicken.
Season with oregano and pepper to taste.
Cover with tight fitting lid and place in oven.
Bake 30 minutes.