In a large pan, heat oil over medium heat and fry the onion until golden brown, about 10 minutes.
Add garlic. Stir and cook 1 minute.
Add tomatoes, pineapple, vinegar, molasses, brown sugar, tomato paste, mustard, paprika, oregano, chipotle powder and pepper. Bring to a boil. Lower heat and simmer, stirring occasionally, for 2 hours, or until thick. Let cool slightly.
Puree the sauce in batches, in a blender, until smooth. Or, use an immersion blender. Keeps in the refrigerator 1 week, or freeze up to 2 months.