Start by combining chopped parsley, cilantro, garlic, oregano, and red pepper flakes in a bowl. Add olive oil and red wine vinegar, then mix well until everything is combined. Season with salt and pepper to taste. Let the sauce sit for a few minutes so the flavors blend properly.

Take your steak and coat it well with the prepared chimichurri sauce. Make sure every side is covered for maximum flavor. Let it marinate for at least 15–20 minutes to absorb the herbs and spices. This step makes the steak juicy and flavorful.

Heat your grill or pan over medium-high heat and cook the steak for about 4–5 minutes on each side. Cook until your desired doneness is reached. Once done, let the steak rest for a few minutes before slicing it thinly across the grain.

In a small bowl, mash or cube the avocado and mix it with lime juice and a few spoons of chimichurri sauce. Stir gently to keep a slightly chunky texture. This adds a creamy, refreshing layer to your quesadilla.

Place a tortilla on a flat surface and sprinkle a layer of cheese on one half. Add sliced steak, avocado chimichurri, and onions. Top with more cheese before folding the tortilla in half. This layering helps everything melt and stick together perfectly.

Heat a skillet with a little oil and place the folded quesadilla in it. Cook for 2–3 minutes on each side until golden brown and crispy. The cheese should be fully melted inside. Repeat the process with remaining tortillas.

Once cooked, transfer the quesadillas to a cutting board. Let them cool slightly before slicing into wedges. Serve warm for the best taste and texture.