Place the chuck steak in a 4 to 6-quart slow cooker and sprinkle with the taco seasoning. Drizzle with the oil and top with the sliced peppers and onions. Pour the water into the slow cooker.
Cover and cook on low for 8 hours. Shred the meat with 2 forks before serving.
Serve with your favorite fajita toppings (and in tortillas, if you'd like).