Cook the rice according to the instructions on the package. Once done, set aside.
Heat the oil in a saucepan on medium heat. Sauté the onion and garlic until they start to turn golden brown. Add in the cumin and sauté for 1 to 2 minutes more. Then add in the black beans with the liquid from the can. Season with salt and bring to a low simmer for 15 to 20 minutes. Taste to adjust the seasoning. Remove from heat and stir in the cilantro. Then set aside.
Heat a sauté pan on medium heat. Brown the beef in the pan with the taco seasoning, breaking it up into smaller pieces until it is no longer pink. Follow the instructions on the taco seasoning. Drain any excess grease from the pan, remove from heat and set aside.
Lay the beef on the tortilla, top with cheese, then rice and black beans. Fold in the ends and roll up.
Heat a nonstick pan on medium heat. Place the burritos seam side down, (one at a time if needed), for about 1 to 2 minutes per side until golden brown. Cut in half and serve with sour cream. Garnish with cilantro, shredded lettuce and diced tomato.