Season steak with 1/2 tsp salt and 1/2 tsp pepper. Grill to the desired doneness, 4-5 minutes per side for medium-rare. Transfer to a cutting board and let rest for 5 minutes before slicing.
Meanwhile, brush both sides of eggplant and peppers with 3 tbsp olive oil. Season with 1/2 tsp salt and 1/4 tsp pepper. Grill until tender, 4-5 minutes per side.
In a small bowl, combine the remaining oil, vinegar, garlic and parsley. Divide the steak and vegetables among individual plates. Spoon the sauce over the vegetables and serve on the side.