In a small bowl, combine the chili powder, cumin, coriander, salt and pepper.
Rub the spice mixture over all sides of the flank steak, place it in the bottom of the slow cooker, and add the soy sauce.
Top the flank steak with the jalapeno, garlic, bell peppers, and onion. There's no need to add any water or other liquid.
Cook on high for 5 to 6 hours or on low for 8-9 hours, or until the steak can easily be shredded with two forks.
Thoroughly drain the meat and peppers, shred the meat and serve on tortillas with toppings or the fixings of your choice.
Notes
To turn this into a freezer meal:In a small bowl, combine the chili powder, cumin, coriander, salt and pepper. Rub the spice mixture over all sides of the flank steak, place it in a gallon-sized freezer bag, and add the soy sauce, jalapeno, garlic, bell peppers, and onion. Close the bag and squeeze out as much air as possible and seal bag closed. Place freezer bag into freezer and it will last 60-90 days. When ready to use, spray inside of slow cooker with non-stick cooking spray and dump ingredients from bag into slow cooker. Place the lid on top and cook for 8-10 hours on low heat (you can cook it for 5-6 hours on high heat, but it will not be as tender as cooking it low and slow. We highly recommend low and slow!). Follow the rest of the instructions as written.