Slather the chicken with the pesto. Heat the olive oil over medium-high heat in a large non-stick pan. Add the chicken and sear for 4 minutes per side. Remove the chicken from the pan and set aside.
Add the pancetta to the pan and sauté until crispy. Add the tomatoes, tomato sauce, rosemary, basil, and oregano and stir. Return the chicken to the sauce and simmer for 20 to 30 minutes, or until cooked through and no longer pink.
Place the cheese on top of each breast, cover, and cook a few minutes more, until the cheese is melted.