1. Place a small sauté pan over medium heat. Add oil. Add sausage and sauté, breaking up into small crumbles until cooked through. Add the onion and sauté a minute or two until softened. Remove to a bowl with all of the pan oil and stir in the breadcrumbs. When mixture cools, stir in the mozzarella. Eyeball the mixture into six portions.
2. Cut slits into chicken breast, to create a pocket, be careful not to cut all the way through. Place a portion of stuffing into the chicken pocket, close with toothpicks. Repeat with the other five breasts.
3. Place breasts in an oiled baking pan, leaving a little space in between each. Brush tops with a little olive oil. Pour white wine into the pan. Bake, 20-25 minutes, until chicken is just cooked through. Run under the broiler a minute if you’d like more color on the skin. Allow breasts to cool several minutes before slicing. Slice breasts on the bias and served topped with spoonfuls of juicy tomato vinaigrette.