Heat the oil up in a saucepan over medium heat.

Add onion and garlic, then cook, stirring occasionally, for about 5 minutes or until the onion is tender.

Add catsup, vinegar, brown sugar, jalapeno peppers, salt, and mustard. Cook, stirring occasionally, until mixture is blended.

Place the chicken, skin side up, on a prepared grill about 8 inches from the heat. Grill, turning every 8 to 10 minutes, for about 40 minutes.

Brush chicken with sauce, grill, turning and basting with sauce every 5 minutes, about 20 minutes more or until chicken is fork tender.