Combine cornstarch, chili powder, GoodSalt, paprika, brown sugar, onion powder, garlic powder, cayenne pepper and ground cumin in a bowl and set aside.

Score steak with cross hatches and rub spices on the meat.  Place in a sealable plastic bag and add olive oil, lime juice and zest, and garlic.  Remove air from bag and seal and make sure marinade covers all of the steak.  Lay flat and set in fridge for 2 hours to overnight.  

In a large cast iron pan or griddle over high heat, add 1 tbl olive oil and let heat up for 1 minute.  Add steak and sear for 3 minutes per side for medium rare.  Remove from pan to plate or cutting board and let rest for 5 minutes.  

While the steak is resting, saute bell peppers and onions in same skillet.  Add more oil to the pan if needed. Cook for 5-6 minutes or until slightly softened. 

Slice the steak into thin slices against the grain.  Serve with warm tortillas and optional garnishes.