Pat the steak dry, then season with olive oil, garlic, salt, and pepper.
Grill or sear on high heat for 3–4 minutes per side for medium-rare. Let rest for 10 minutes, then slice thinly against the grain.
Make Cheese Crisps:
Heat a nonstick skillet over medium heat. Place small piles of shredded cheese and cook until melted and crispy. Transfer to parchment paper to cool.
Prepare Chimichurri Sauce (if homemade):
Mix parsley, oregano, garlic, olive oil, red wine vinegar, red pepper flakes, salt, and pepper. Taste and adjust seasoning as needed.
Toast the Bread:
Lightly butter each slice and toast on a griddle or skillet until golden brown.
Assemble the Sandwich:
Spread chimichurri on the bottom slice of bread.
Add a layer of sliced steak.
Top with diced red onion.
Place cheese crisps on top for crunch.
Add another layer of chimichurri if desired, then close with the top slice of bread.
Serve:
Slice in half and serve warm with fries, a side salad, or your favorite chips.
