Slice the flank steak into thin strips across the grain.
In a small bowl, combine the cumin, chili powder, 0.125 tsp sea salt, and black pepper.
Rub the spice blend evenly over the steak strips.
Heat the olive oil in a cast-iron skillet over medium-high heat.
Add the steak to the skillet and sear for 2-3 minutes per side until browned and sizzling.
Remove the steak from the pan and set aside.
In a small bowl, mash the avocado with lime juice and the remaining 0.125 tsp sea salt until creamy.
Place the corn tortillas in the skillet and sprinkle the Monterey Jack cheese over one half of each.
Top the cheese with the cooked steak strips and fold the tortillas in half.
Cook for 1-2 minutes per side until the tortillas are toasted and the cheese is melted.
Serve the quesadillas topped with fresh guacamole and chopped cilantro.