Heat up oil on medium heat in a skillet. Brown the onion and garlic for about 5 minutes. Add the cumin and chili powder, cooking until the spices become fragrant.
Add the ground beef/pork. Cook until the meat is no longer pink. Stir in the tomato paste, soy sauce, sake or substitute. Cook a few more minutes until most of the liquid has evaporated. Season with black pepper, to taste.
To serve: Spoon some of the cooked sticky rice on a plate. Top with taco meat mixture and the garnishes of choice. Alternatively, the mixture can be served in taco shells as we did (corn tortillas shells were preferred over flour this time). Tostada shells are another option, too.