In a 4 or 5 quart Dutch oven over medium-high heat, heat 1 teaspoon of the oil. Add bacon and cook until browned and crisped. With a slotted spoon remove bacon to a medium bowl. Leave the drippings in the skillet.

Season the chicken with ½ teaspoon of the salt and ¼ teaspoon of the pepper. Cook the chicken in batches; add half of the chicken pieces to the Dutch oven and cook until golden brown. With a slotted spoon remove chicken pieces to the bowl with bacon. Repeat process with remaining chicken pieces.

Leave any drippings in the Dutch oven and add the remaining 1 teaspoon oil over medium-high heat. Add onion and cook stirring frequently, for 2 minutes. Add garlic, mushrooms and Rosemary and cook while stirring until the mushrooms begin to soften, about 2 minutes.

Add balsamic vinegar and cook while stirring until some of the balsamic vinegar has evaporated, about 1 minute.

Add tomatoes, tomato paste and bay leaf to the Dutch oven along with the reserved bacon and chicken; stir to combine. Season the sauce with the remaining 1 teaspoon salt and ½ teaspoon pepper. Cook over medium-high heat while stirring until the sauce bubbles. Let bubble for 2 minutes. Reduce heat to low, cover and simmer for 30 - 40 minutes until the sauce has slightly thickened.

Meanwhile, start boiling a large pot of lightly salted water. Add spaghetti and once it comes to a full boil, cook for 8 - 10 minutes until al a dente (or follow package directions). Drain spaghetti, ladle portions of spaghetti into serving plates or bowls and top with chicken cacciatore sauce. Garnish each serving with parsley and grated Parmesan cheese.