Heat the oil in a pot over medium heat. Add the onions and garlic and cook until tender, about 3-4 minutes. Stir in the remaining ingredients, except pork chops. Reduce the heat to medium-low, cover and very gently simmer the sauce for 20 minutes, stirring occasionally. Thin the sauce with a little water if it becomes too thick. Reserve on low heat until the pork chops are cooked. Preheat barbecue or indoor grill to medium-high heat. Lightly oil the grill. Season pork chops with salt and pepper, and then 3-4 minutes per side, or until cooked through. Brush chops with barbecue sauce and serve extra sauce along side for dipping.
Note: Chipotle peppers can be found in cans in the Mexican food aisle. Store the unused peppers in a tightly-sealed jar in the fridge. Keep any leftover barbecue sauce in the fridge and use to top other meats such as burgers or chicken.