Just lay the chicken inside. Bake for 20 minutes or until the chicken has an internal temperature of 165°F. Boneless, skinless thighs cook quickly. Check after 20 minutes, and if they are not quite up to temperature, put back in the oven and continue cooking and checking the temperature in 5-minute increments.ust lay the chicken inside. Bake for 20 minutes or until the chicken has an internal temperature of 165°F. Boneless, skinless thighs cook quickly. Check after 20 minutes, and if they are not quite up to temperature, put back in the oven and continue cooking and checking the temperature in 5-minute increments.