Place the beef roast into the slow cooker with the chili powder, cumin, salt and pepper and water/broth. Set on low and cook for 8 hours. Once finished cooking, remove the meat from the liquid and pull apart and shred with 2 forks.
In a mixing bowl, toss together the cabbage, apple pieces, shredded carrots.
In a small resealable container, add the olive oil, vinegar, cumin, salt and pepper. Shake, shake, shake. Then pour over the cabbage mix.
To serve, spoon some shredded beef onto the buns and top with the slaw. Use small dinner rolls for "sliders," or regular buns for sandwiches.
Serve with a side of fresh fruit, or as is. (Just the sandwich itself was meal enough for me!)