Season both sides of chicken breasts with garlic salt and pepper.
Heat the olive oil in a skillet over medium heat; when hot, brown the chicken in the skillet, about 3 to 4 minutes per side. Add onion; cook and stir until onion is browned, 3 to 4 minutes.
Pour the diced tomatoes and balsamic vinegar over the chicken; season with basil, oregano, rosemary, and thyme. Simmer until chicken is no longer pink and the juices run clear, about 12-15 minutes.
Serve with rice, mashed potatoes, vegetables or salad for a healthier option.