In a small bowl, combine the garlic dijon mustard ingredients.
Add the chicken breasts, diced butternut squash and the garlic cloves. Toss to coat.
Remove only the butternut squash from the marinade and place on one half of the baking sheet that's been been sprayed with non-stick baking spray. Bake for 15 minutes.
Let the chicken marinate while the butternut squash bake.
Remove the baking tray from the oven and add the chicken breasts and garlic cloves on the other half of the tray.
Return the baking tray back to the oven and cook for 25 minutes or until the chicken reaches an internal temperature of 165°F.
Serve immediately.
Notes
About halfway through the cooking, remove the baking tray and flip the chicken.