Preheat grill to med-high heat. Brush steak with olive oil on both sides, then season with salt and pepper.
Once grill is preheated, grill steak for 2-3 min on either side, depending on thickness of steak and the way you like yours cooked.
Remove steak from grill and let rest for 5-10 min before slicing against the grain.
Meanwhile, mix together honey dijon sauce.
Toast mini pitas in oven ahead of time for 4-5 min if desired, then top each mini pita with honey dijon sauce, arugula, thinly sliced red onion, 2-3 steak slices then shaved parmesan cheese.