Heat oil in large sauce pan (at least 4 inches deep) over moderate heat until hot, add the onion, celery, and bell pepper and cook about 5 minutes, until softened. Add garlic+salt mash, pepper and meat, and cook until meat is no longer pink, about 5 minutes.
Purée tomatoes with juice, ketchup, molasses, vinegar, and Worcestershire sauce in blender until smooth then add to meat and simmer, uncovered, stirring occasionally until sauce is thickened, about 25 minutes. Serve on toasted buns.