Prepare grill. Sprinkle both sides of steak with salt. Grill 5 minutes per side or until desired degree of doneness; let stand 5 minutes. Slice into 1/4-inch-thick strips. Chop 1 chile, and combine with 1 teaspoon adobo sauce, yogurt, onions, cilantro, and lime juice in a bowl. Divide steak strips among bottom halves of rolls; top each portion with 2 tablespoons sauce mixture and, if desired, pepper slices.