Chop parsley and cilantro. Mince shallot and garlic until fine.
Stir herbs with oregano, red pepper flakes, vinegar, lemon juice, salt, and pepper.
Drizzle in olive oil while stirring until emulsified. Add warm water to loosen if desired. Let sit 10 minutes.
Pat steak dry. Season all over with salt and pepper, then rub lightly with olive oil.
Heat a cast-iron skillet or grill over high until very hot.
Sear steak 3–4 minutes per side for medium-rare. Add butter in the last minute and baste, if using.
Rest steak 5–10 minutes. Slice against the grain and spoon chimichurri over the top.
Notes
Try adding a chopped Fresno chili to the sauce for gentle heat, or swap cilantro for more parsley if you prefer. Leftover chimichurri keeps 4–5 days refrigerated in a sealed jar; bring to room temperature and stir before serving.This recipe is an original creation inspired by classic Chimichurri Steak Made Easy flavors. All ingredient ratios and instructions are independently developed.