Cut flank steak into 6 portions. In a crockpot combine meat, onion, green pepper, red pepper, jalapeno, cilantro, garlic, chili powder, cumin, coriander, and salt. Add tomatoes. Cover and cook on low 8-10 hours or high for 4-5 hours. Remove meat from crockpot and shred. Return to crockpot and stir. To serve spread on tortillas top with toppings and roll up tortilla.