Slice the grapefruit, orange, and lemon into 1/4-inch rounds.
Place them in a large resealable bag.
Add the chicken breasts to the bag.
Combine orange juice, olive oil, Dijon mustard, vinegar, salt, and pepper to make the marinade.
Pour this over the chicken with citrus slices.
Seal the bag and refrigerate for 6 to 8 hours.
Preheat the oven to 350 degrees Fahrenheit.
Take the chicken out of the marinade, shaking off excess liquid.
Place on a baking dish.
Cook the chicken in the oven for about 25 to 30 minutes, ensuring it’s properly cooked through.
Rotate the chicken halfway for even cooking.
Once cooked, let the chicken rest for a few minutes before serving.