In a small bowl, mix the sambal oelek with the canola oil, Dijon mustard and garlic. Place the chicken in a resealable plastic bag and pour in the sambal mixture. Seal the bag and massage the marinade into the chicken until it is well coated. Let stand at room temperature for 1 hour.
Preheat the oven to 400°. On a large rimmed baking sheet, arrange the chicken thighs skin side up. Season the skin with salt and pepper and roast for about 45 minutes, until the chicken is cooked through and the skin is browned and crisp. Transfer the chicken thighs to plates and serve.