Preheat oven to 425 degrees F. Line a large rimmed baking sheet with foil and set aside.
Season chicken thighs on both sides with salt and pepper, then drizzle 1 tbsp olive oil all over prepared baking skeet. Arrange chicken thighs skin-side down on baking sheet in single layer.
Toss the carrots, brussels sprouts and onion with the remaining 1 tbsp olive oil and 3 tsp garlic. Season with salt and pepper to taste, then spread the veggies around the chicken thighs, making sure to not over crowd the pan.
Roast for 25 minutes, then carefully remove the pan from the oven and flip the chicken thighs over, so they are skin-side up. Brush the tops of the chicken with bbq sauce, and stir the veggies around as well. Roast for an additional 7 minutes. Remove from the oven and brush one more time with more sauce and roast for an additional 7 minutes, or until the sauce starts to caramelize and the chicken is cooked through.
Serve the roasted chicken thighs with the veggies and enjoy!
Notes
Chicken thighs come in all shapes and sizes, so make sure you use an instant read thermometer to check the internal temperature of the chicken. It should read 165 degrees F. when complete.