For the blackened hanger steak: Mix together the paprika, onion powder, garlic powder, salt, cayenne, chili powder and black pepper in a bowl. Rub the mixture over the hanger steaks and put the steaks on a wire-racked baking sheet. Place in the fridge overnight.
For the chimichurri sauce: In a food processor, add the parsley, cilantro, red wine vinegar and garlic. Pulse until combined but still a bit coarse, about 10 pulses. Add in the crushed red pepper, and then slowly drizzle in the oil and pulse about 5 more times. Season with salt and pepper and set aside for the flavors to meld. (The chimichurri can be made up to 3 days in advance.)
For the sweet fried plantains: Heat the vegetable oil in a large skillet over medium heat. Add the plantains in batches, taking care not to overcrowd the pan. Fry each side until dark brown. Using a spider, remove the plantains and drain on paper towels. Season with garlic salt when still hot.
To cook the steaks, heat a large cast-iron skillet over medium heat. Add the vegetable oil and sear all 4 sides of the hanger steaks until crusty and dark, 4 to 5 minutes each side. The steaks are done when an instant-read thermometer reads 135 degrees F. Let rest for 5 minutes before slicing.