Step 1: Make the Chimichurri Sauce

In a medium bowl, combine the chopped parsley, fresh cilantro, minced garlic, oregano, and red pepper flakes. Stir in the red wine vinegar and olive oil. Mix well until it becomes a rich, herby sauce. Season with salt and pepper to your taste.

Pro tip: Let the chimichurri sit for at least 15 minutes to allow the flavors to meld. It can also be made a day ahead for even more flavor.

Step 2: Marinate the Steak

Pat the steak dry and season both sides with salt and pepper. Place the steak in a shallow dish or zip-lock bag and pour over enough chimichurri sauce to coat generously. Cover and refrigerate for at least 30 minutes, or up to 12 hours if you’re prepping ahead.

This step is key to infusing the meat with bold, tangy flavor.

Step 3: Grill the Steak

Preheat your grill or a cast-iron skillet over medium-high heat. Grill the steak for 4–5 minutes per side for medium doneness. Once grilled, remove it from the heat and let it rest for 5–10 minutes before slicing it thinly across the grain.

Resting the steak locks in juices, keeping it tender and flavorful.

Step 4: Prepare the Avocado Chimichurri

In a small bowl, mash the ripe avocado with a fork. Add lime juice and 3 tablespoons of the reserved chimichurri sauce. Mix until smooth and creamy. Taste and adjust seasoning if needed.

This adds a fresh, velvety texture and citrusy brightness to the quesadilla.

Step 5: Assemble and Cook the Quesadillas

Heat a large nonstick skillet over medium heat. Place one tortilla flat in the pan. Sprinkle a generous layer of shredded Monterey Jack cheese over half of the tortilla. Add sliced steak, a spoonful or two of avocado chimichurri, and a few onion slices. Top with more cheese and fold the tortilla over into a half-moon.

Cook for 2–4 minutes per side, until golden and crispy on the outside and the cheese is melted inside. Repeat with remaining tortillas and filling.

Slice into wedges and serve hot!