Combine the chimichurri ingredients, setting aside ½ cup for salad dressing. Combine sauce with steak and marinate for at least 3 hours, covered and chilled. If using vegetables instead of steak, prepare veggies to your liking and dress while still warm.
Meanwhile, toss corn and tomato salad ingredients with ¼ cup of reserved dressing and set aside.
Remove steak from fridge, pat dry, and grill to taste. Let the meat rest before carving, dress with remaining ¼ cup sauce, and serve.