In medium bowl, whisk broth and seasoning. In 5- to 6-quart slow cooker, add steak, onion and broth mixture; cover and cook on high 4 hours or low 8 hours or until steak is very tender and falls apart. With 2 forks, shred steak in slow cooker.
Preheat oven to 400°; spray rimmed baking pan with cooking spray. Spread chips on prepared pan; top with cheeses and steak mixture. Bake nachos 12 minutes or until golden brown and cheese melts. Makes about 9 cups.