In a medium skillet, heat the canola oil over medium heat. Add the onion and garlic. Cook, stirring occasionally, until cooked through but not browned, about 5 minutes. Transfer to a food processor. Add the black beans, chipotles in adobo, and this is where I like to add about a spoonful of that lovely adobo sauce but this is optional. Also add the cumin, plus salt and pepper to taste. Process until nicely blended but not totally smooth.