Salt flank steak both sides. In a pan, add oil and heat to high. Add flank steak and sear til golden brown on both sides about 2 minutes each side.
Add steak to crock pot. In remaining oil in pan add tomatoe paste and chicken stock and mix til paste is melted. Add pepper, oregano, cumin, garlic to pan and mix until incorporated with paste. Pour over flank steak.
Add bell pepper, oregano and onion to crock pot. Mix and set to low for 6 hours.
After done, remove meat and shred with 2 forks. Put back into crock pot and mix with remaining ingredients. Serve over rice or make tacos with tortillas. Yum!
If you choose to do this in the oven in a Dutch oven dish... sear meat in Dutch oven in oil on both sides. Add the rest of the ingredients and place in oven for 2.5 to 3 hours on 325°F.