Cut flank steak into 6 portions. In any size crockpot, combine meat, onion, bell peppers, jalapeno pepper, cilantro, garlic, chili powder, cumin, coriander, and salt. Add tomatoes. Cover and cook on low for 8-10 hours or on high for 4-5 hours. Remove meat from crockpot and shred. Return meat to crockpot and stir.
To serve fajitas, spread meat mixture into flour tortillas; add favorite toppings and roll up tortillas.