Season the steak on both sides with paprika, chili powder, garlic powder, half of the cumin, and season with salt and pepper. Set aside.
For the Salsa Verde: Place tomatillos in a pan and cover with water, place on medium high heat. Bring to a simmer for 5 minutes turning the tomatillos over about half way through cooking. Once soft drain well and place in blender or food processor along with garlic, cilantro, lime juice, the remaining cumin, and season with salt and pepper. Blend until smooth. Then refrigerate in a shallow bowl to cool completely.
Heat the oil in a cast iron or nonstick pan on medium heat. Cook the steaks on both sides until your desired temperature is reached using a thermometer (see below). Once cooked set aside on a cutting board to rest for 3 - 5 minutes. Then slice thin against the grain of the meat.
Place lettuce in the taco shell, then sliced steak, diced tomato, salsa, and sour cream. Garnish with cilantro.