In a slow cooker, place the boneless beef roast. Dice the onion and place over the beef roast. Season the top of the roast and onions with the steak seasoning. Put the crock pot lid on the roast and turn on med-high heat. Cook the roast for 5-6 hours, or until the roast shreds easily. Once the roast is ready to shred, remove some of the excess fat and discard. If there is too much juice, drain some of the juice from the roast (don't discard, but keep in case you need to add it back to the meat). To the meat, add the diced green chilies, diced tomatoes, salt, cumin, Mojito lime seasoning and chili powder. Shred the meat and season as desired or needed. Serve as a taco or burritos with shredded cheese, lettuce, tomatoes and sour cream.