Add lime juice, 2 Tbsp olive oil, minced garlic, chili powder, cumin, and ½ tsp salt to a large ziplock bag and place flank steak in the bag. Make sure marinade is distributed evenly and place in fridge for at least 2 hours to marinate.
Heat grill pan or large cast iron pan until extremely hot and placed flank steak on it. Grill for 3 minutes on each side. If you want criss-cross grill marks, be sure to rotate steak after 1.5 minutes on each side.
Remove steak to cutting board and let cool slightly. Slice flank steak in strips, being sure to cut against the grain.
While steak is cooling, heat pan to medium and add 1 Tbsp olive oil. Add onions, remaining ¼ salt, and ¼ tsp pepper and cook for about 5 minutes. Add sliced jalapeño and cook for another 6-8 minutes, until onions are browning.
Wipe out pan. Lightly brush one side of all tortillas with remaining olive oil and place one oil-side down on pan over medium heat. Sprinkle gorgonzola cheese over the top, top with steak, onions and jalapeño, and a little more cheese.
Place another tortilla over the top, cook for about one minute, and then flip and cook for another two minutes. Be sure to rotate tortillas halfway through cooking if you want criss-cross grill marks. Continue with remaining tortillas and filling.
Using a pizza cutter, slice quesadillas into four and serve with mashed or sliced avocado.