Start by making the Chimichurri Sauce. Put the oregano, marjoram, and parsley on a wooden board and finely chop. Put the Jalapeño and garlic in a ceramic bowl along with the chopped herbs.
Pour in the red wine vinegar and olive oil, stir well, and season to taste with salt and pepper. Cover and leave in the fridge until ready to use, so the flavors can mingle, then bring to room temperature when ready to serve.
For the Prairie Rub: Put all the ingredients in a bowl and mix together. Store the rub in a glass jar with a tight-fitting lid for up to 6 months.
Wash the steak and pat dry with a paper towel. Drizzle with oil and sprinkle the steak on both sides with the Prairie Rub. Season with salt and pepper, cover, and refrigerate for 6–24 hours.
After this time, remove the steak from the fridge and let it come to room temperature. Heat a barbecue to medium–high. Place the steak on the barbecue and cook for 8–10 minutes on each side for rare and continue to cook if you prefer medium to well done.
Remove the steak from the grill, cover, and let it rest for 10 minutes. Carve and serve with the Chimichurri Sauce.