Brush steak with olive oil and season with salt and pepper.
Rub the surface of the grill pan with butter.
Place ribeye on a hot grill pan with tongs, pressing down for great grill marks. Cook on one side for 1 minute and 45 seconds, then rotate the steak 90 degrees. After 2 minutes, flip the steak and cook for an additional 1 minute and 45 seconds. Rotate 90 degrees and finish cooking for 2 minutes. Ensure the steak is cooked until its internal temperature reaches 145°F on a meat thermometer for medium doneness, before removing from grill.
Let steak rest for 7-10 minutes.
Add all the chimmichurri ingredients into a food processor and pulse until smooth.