Heat the olive oil in a large skillet. Add the sliced prosciutto and fry for about 2 minutes. Finely chop the peeled onion and garlic and toss in the skillet, add the sage and rosemary, fry for 3-4 more minutes.
Add the chicken breasts. Season with salt and pepper, fry for 5 minutes over medium heat, turning until meat begins to brown on both sides and onions caramelise on the bottom of the skillet.
Remove the chicken and set aside in a warm place. Increase the heat and pour the wine into the sauce, cook for 2 minutes for the wine to evaporate. Reduce the heat and add the tomatoes, while trying to mash them with a spoon in the process, add the tomato paste and halved mushrooms. Cover and simmer for 15-20 minutes until sauce thickens and reduces slightly. Season with salt to taste. Add the fried chicken breasts and cook the dish uncovered for about 15 minutes.
Serve sprinkled with parsley.