Season chicken with salt and pepper. Heat 3 tbsp. of oil in a large heavy bottomed skillet. When the oil is hot and just starting to smoke carefully add the breasts. Sear until golden brown, 7-9 minutes. Carefully turn the breasts over and continue to sear until chicken is fully cooked. Chicken is done when an instant read thermometer is inserted into the thickest part and it reads 165 degrees. Transfer chicken to a plate and set aside. Add remaining 1 tbsp. of oil, turn heat down to medium, and then add zucchini, summer squash and onion, season with salt and pepper. Cook for 3 minutes moving around the skillet. Add rosemary, garlic and tomatoes, cook for 1 minute continuously stirring. Add lemon juice, stirring to incorporate then add the chicken and cook another minute or so to re-warm the chicken. Serve and Enjoy!