To begin, cut the flank steak in half cross-ways. Sprinkle each half with ½ teaspoon each of the salt, freshly ground black pepper, and garlic powder. Lightly spray the inside of your slow cooker with cooking spray and then stack the steak halves inside.
Cut the red onion, green bell pepper, and sweet red bell pepper into strips (discarding the seeds and stems of course.) Toss the strips into the slow cooker on top of the flank steak.
In a mixing bowl, combine the soy sauce, tomato paste, minced garlic, grated ginger, and cola. Whisk these together. If you would like a little “heat,” add in the red pepper flakes.
Pour the sauce over the contents of the slow cooker. Cover and cook on low for 6-7 hours. Carefully remove the steak pieces to a cutting board and shred it with two forks. Return the shredded meat to the slow cooker and stir it in with the peppers and onion.
Serve wrapped in flour tortillas with some sour cream or guacamole if you like.