Heat the oil in a saucepan over medium heat. Add the onion and garlic and cook for 5 minutes, until the vegetables soften. Add the tomato sauce, chipotle, maple syrup, water, vinegar, tamari, salt, and pepper, stirring to mix well. Simmer for 20 minutes, or until the sauce reduces to the desired consistency. Near the end of the cooking time, stir in the liquid smoke, then taste and adjust the seasonings, adding more salt, maple syrup, or vinegar if needed to balance the flavors.