Season 2 lb ribeye steak with salt and black pepper.
Sear steak on high for 3 minutes each side, then finish to preferred doneness (125°F for medium rare).
Combine 1 bunch chopped parsley, 1 tsp chili flakes, 1 tsp oregano, 4 minced garlic cloves, 3 tbsp red wine vinegar, and ½ cup olive oil for chimichurri; refrigerate.
Rest steak, then slice thinly.
Sauté 1 sliced medium sweet onion until caramelized.
Assemble sliders: slider bun, slice of provolone, onions, steak slices, chimichurri, another slice of provolone, bun top.
Grill until cheese melts.
Serve with extra chimichurri sauce.