Heat the oil in a large nonreactive saucepan over medium heat. Add the garlic and saute until softened, but not brown. Add in the roasted onion.
Stir in the ketchup, tomato sauce, 1 cup water, vinegars, Worcestershire sauce, lemon juice, hot sauce, molasses, sugar, both mustards, spices, salt and black pepper and bring to a boil. Reduce the heat to low and simmer, uncovered, until thickened, about 15 minutes, stirring often to prevent scorching. If the sauce becomes too thick, add a little water. Remove from heat.
Stir the beans and 1 cup of the sauce together. Garnish with scallions.