Preheat your grill to medium-high heat. In a small bowl, mix olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper. Rub this mixture all over the flank steak.
Grill the steak for about 5-7 minutes on each side, or until it reaches your desired doneness. Remove from the grill and let it rest for 5 minutes before slicing it thinly against the grain.
While the steak is resting, prepare the avocado chimichurri. In a blender or food processor, combine cilantro, parsley, red wine vinegar, red pepper flakes, avocado, lime juice, and salt. Blend until smooth.
To assemble the quesadillas, place a tortilla on a flat surface. Sprinkle half of the tortilla with 1/2 cup of shredded cheese, add a layer of sliced steak, and top with another 1/2 cup of cheese. Fold the tortilla in half. Repeat with the remaining tortillas.
Heat a large skillet over medium heat. Cook each quesadilla for about 3-4 minutes on each side, or until the tortillas are golden brown and the cheese is melted.
Slice the quesadillas into wedges and serve with the avocado chimichurri drizzled on top or on the side for dipping.