Set a 12-inch saute pan over medium heat and add the olive oil. Once hot, place the onions in the pan and saute until translucent, 3 to 4 minutes. Add the garlic and cumin to the pan and continue to saute until fragrant, about 1 minute. Add the beef to the pan and cook, breaking the pieces up as they cook, until the meat is browned, about 8 to 10 minutes. Season with the chipotle pepper and the salt. Add the beef broth and tomato paste to the pan and bring to a simmer. Cook the meat, stirring occasionally until most of the liquid has evaporated, about 20 minutes. Remove from the heat and serve with the garnishes for guests to assemble their tacos to their liking.