Place steaks on edges and cut lengthwise to within 1-inch of opposite edges. Spread steaks even and flatten to an even ¾ inch thickness with a meat-pounder (cover with plastic wrap). Rub insides with the chile powder. Let steaks sit at room temperature while preparing stuffing.
In a large skillet over medium heat sauté chilies, onions, and garlic in the oil until onions are transparent, stirring occasionally. Remove from heat and cool to room temperature.
Season butterflied steaks with salt and pepper. Divide stuffing mixture and spread on the bottom half of each steak. Sprinkle with a portion of the cheese. Fold steaks over to enclose stuffing and secure with skewers (if not metal skewers, soak wood in water 20 minutes then wipe dry before using).
Grill over hot coals about 14 minutes total for rare (or broil in oven), or until desired doneness, turning once. Let steaks sit 3-5 minutes then cut across grain (removing skewers).
Serve with salsa and chopped onion tops or chives. Enjoy!!!