Spray a 9 x 13 inch baking dish with cooking spray, then add your chicken breasts.
Lightly salt and pepper both sides of each breast.
Stir together pesto sauce, mustard, vinegar, chicken broth and entire can of tomatoes with juice.
Spoon the sauce mixture over and around the chicken breasts.
Bake in a preheated 425 degree oven for 30 minutes, then turn the oven temperature down to 400 degrees, and cook an additional 10 minutes, or until internal chicken temperature reaches 165 degrees Fahrenheit. If your chicken breasts are thin, it may not take this long for them to bake, so use your meat thermometer to check for doneness.
When you take it out of the oven, use a large spoon or measuring cup to scoop up the juicy sauce in the dish and baste it all over the chicken breasts, so they will be extra nice and juicy. Also let the chicken rest for 5 or so minutes before serving, so the juices inside will redistribute.
Tips to note: If your oven tends to run extra hot, bake at 400 degrees Fahrenheit the entire time, instead of 425 degrees Fahrenheit. Also, how long you cook your chicken breasts totally depends on how thick they are. The thicker the chicken breast the longer you have to bake them. If they’re thin, the less time. Just make sure the inside of the chicken breast reaches 165 degrees Fahrenheit. Don’t bake these on the top rack in your oven if it’s close to the broilers, because the mixture on top will burn before the chicken is cooked properly. Bake it more in the middle of the oven.