Step 1: Make the Chimichurri. In a bowl, mix the red wine vinegar, olive oil, diced shallot, chopped parsley, chopped coriander, garlic, chili, oregano, salt, and pepper. Stir everything together and set it aside to let the flavors meld.
Step 2: Prepare the Steak. Season the steaks with your steak seasoning. Heat a frying pan or grill pan over medium-high heat. Cook the steaks for 3-3.5 minutes on each side for medium-rare, or adjust the time to your preferred doneness. Once cooked, let the steaks rest for 5 minutes, then slice them thinly against the grain.
Step 3: Assemble the Tacos. Warm your tortillas in a pan or microwave. Spread a layer of mashed avocado on each tortilla. Add a few slices of steak, drizzle with chimichurri, and finish with a sprinkle of crumbled feta.
Step 4: Serve. Plate the tacos and enjoy them with your favorite sides or as they are!