In a small bowl, whisk together the olive oil, dijon mustard, lemon juice, fresh thyme, salt, ground black pepper and minced garlic until combined.
Add the chicken thighs to a large bowl. Pour ⅔ of the olive oil mixture over the chicken thighs. Toss until the chicken is completely coated. Let the chicken marinate in the refrigerator for at least 20 minutes (6 hours is best).
Place the brussel sprouts, sliced red onion and sliced lemon in a medium bowl. Toss with the remaining olive oil mixture until well coated.
Pour the vegetables out onto a sheet pan.
Once the chicken has finished marinating, nestle the chicken thighs into the vegetables.
Bake at 425F for 30-40 minutes, until the chicken reaches an internal temperature of 165F. For crispy skin, turn the oven to broil for 3-5 minutes at the end.
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Notes
We prefer bone-in skin-on chicken for this recipe as it creates a really juicy and flavorful chicken. If you use a different cut of chicken, you may need to adjust the cook time accordingly.
For extra crispy skin, broil the chicken for 3-5 minutes at the end of the baking time.
If you do not like red onion, a yellow onion or sweet onion works just as well.
If you love a more intense lemon flavor, add the chopped up zest of one lemon to your marinade.