I found this recipe on Cafemom, I am copying and pasting so you don't have to join a group to see it.
A cowboy steak is a rather thick (2-inches) cut of meat. It lends itself well to searing first, to get browning, then slower cooking with either indirect heat on the grill, or in the oven.
Yield: Serves 3 - 4.
1.) 1 2-lb "Cowboy Steak" (frenched beef rib steak)
1.) 1-1/2 cups firmly packed fresh flat-leaf parsley, trimmed of thick stems
2.) 4-6 garlic cloves
3.) 3 Tbsps fresh oregano leaves
4.) 3 Tbsp red or white wine vinegar
5.) 3/4 cup olive oil
6.) 1-1/2 teaspoon sea salt
7.) 1/2 teaspoon red pepper flakes
8.) 1/4 teaspoon freshly ground black pepper
1. Prepare the chimichurri sauce/marinade. Finely chop the parsley, garlic and oregano (can do with a food processor), place in a small bowl. Stir in the vinegar, oil, salt, pepper, and red pepper flakes. Set aside two thirds of the sauce for serving with the steak (cover with plastic wrap and let sit at room temperature). The remaining third of the sauce will be for the marinade.
2. Place steak in a bowl or large ziplock bag. Take about a third of the prepared chimichurri sauce and coat the steak for a marinade. Cover completely with plastic wrap or remove air from ziplock bag and secure close. Let steak marinate for several hours. Remove steak from refrigerator 2 hours before cooking so that it gets close to room temperature before cooking. Right before cooking, wipe off marinade from steak and sprinkle steak generously with salt and pepper.
3a. Grilling Instructions Prepare grill so that one side has high, direct heat and another side has indirect heat. Brush grill grates with vegetable oil. Place steak first on the side of the grill with high, direct heat, so that it sears. Grill for a minute or two on each side, enough to brown the meat. Then transfer the steak to the indirect heat side of the grill. Cover the grill, try to maintain a grill temperature of 350°F. Cook for 5-10 minutes (or more) until the steak is cooked to your desired level of doneness. You can use the finger test to check for doneness, or a meat thermometer. For rare, pull the meat off the gril at an internal temp of 120°F. For medium rare, 125-130°F. Remove the meat to a plate and cover with aluminum foil. Let rest for 5 minutes before serving.
3b. Stovetop/Oven Instructions Preheat oven to 350°F. Heat a large cast iron skillet on medium high to high heat. Hold the steak fat-side down to render a little of the fat into the pan. Then sear each side until nicely browned, about a minute or two each. Transfer the steak (if using cast iron pan, can place the whole pan in the oven) to the oven to finish to desired doneness, anywhere from 5 to 15 minutes, depending on the thickness and size of the steak and how well done you like it. You can use the finger test to check for doneness, or a meat thermometer. For rare, pull the meat out of the oven at an internal temp of 120°F. For medium rare, 125-130°F. Remove the meat to a plate and cover with aluminum foil. Let rest for minutes before serving. Serve steak with remaining chimichurri sauce.
This is a fairly simple recipe. My husband doesn't really love parsely like I do, so I did marinate the steak in the chimchurri. But I did not serve it with the steak. We liked this, but I don't think I marinated it long enough because it was still a bit tough. If I made it again I might use a tad meat tenderizer.
I served this with mashed potatoes and refried beans that I made using leftover kidney beans, black beans, salt and pepper, cumin and coriander. I mashed them in a skillet and heated.