1-Step 1: Mix the chimichurri sauce Start by combining the parsley, cilantro, garlic, oregano, red pepper flakes, red wine vinegar, olive oil, salt, and pepper in a bowl. Stir well so the herbs and garlic are evenly coated. Let the sauce sit for 30 minutes before using it. This resting time helps the flavors blend and settle into something bold and fragrant. If you are making dinner for a mixed crowd, keep the red pepper flakes on the lighter side. That way the sauce still brings warmth without overwhelming younger eaters or spice-sensitive guests. The sauce should taste bright, herby, and punchy.

2-Step 2: Season and marinate the steak Pat the steak dry, then season both sides with salt and pepper. Spoon enough chimichurri over the steak to coat it well, then set it aside to marinate for at least 30 minutes. If you have extra time, let it sit for up to 4 hours for deeper flavor. A short marinade works fine too, especially on busy nights. Flank steak, skirt steak, and sirloin all work well here. Thin cuts absorb the chimichurri quickly and grill fast, which makes this chimichurri grilled steak quesadilla a strong choice for cooks who want flavor without a long wait.

3-Step 3: Grill the steak Preheat your grill to medium-high heat. You want a hot grate so the steak picks up good sear marks right away. Grill the steak for 4 to 5 minutes per side for medium-rare, depending on thickness. If your cut is thicker, give it a little more time and check the internal temperature as needed. For best results, do not move the steak too soon. Let it sit on the grill and build that dark, flavorful crust. That crust brings the smoky character that makes the grilled steak quesadilla taste like something made over a backyard flame.

4-Step 4: Rest and slice the steak Once the steak is done, transfer it to a cutting board and let it rest for several minutes. Resting keeps the juices inside the meat instead of spilling out when you slice it. After resting, slice the steak thinly against the grain. Thin slices are easier to layer into the quesadilla and stay tender in every bite. If you want to prep ahead, this step can be done earlier in the day. Just chill the sliced steak, then warm it briefly before assembling the quesadillas.

5-Step 5: Make the avocado chimichurri In a small bowl, mash the ripe avocado until mostly smooth. Stir in 1/4 cup of the prepared chimichurri sauce and the juice of 1/2 lime. Mix until creamy, then season with salt and pepper to taste. The result should be rich, green, and slightly tangy, with enough body to spread easily. This avocado chimichurri is what gives the quesadilla its lush, velvety layer. It softens the sharper flavors of the sauce and adds a cool contrast to the hot steak and melted cheese.

6-Step 6: Build the quesadilla Lay one tortilla on a clean surface. Sprinkle half the cheese over one side, then add 1/2 cup thinly sliced grilled steak, 1/4 cup avocado chimichurri, and 1/4 cup sliced onion. Top with the second tortilla and scatter the remaining cheese on top so it melts into the layers as it cooks. This setup gives you a sturdy quesadilla with plenty of flavor in every section. For a more colorful version, add a few strips of bell pepper or a spoonful of diced tomato. Those additions keep the quesadilla fresh and lively while still letting the steak and chimichurri lead the way.

7-Step 7: Cook until golden and crisp Heat a skillet over medium heat. Place the assembled quesadilla in the skillet and cook for 2 to 4 minutes per side. Press lightly with a spatula so the tortilla browns evenly and the cheese melts. When the outside is golden and crisp and the filling is hot, transfer it to a cutting board. Let it sit for a minute before slicing. That short pause helps the cheese set a little so the wedges stay neat. Cut into triangles and serve warm, with extra chimichurri or a little avocado chimichurri on the side if you like more sauce.