Thinly slice the flank steak against the grain into small, bite-sized strips.
In a small bowl, toss the steak strips with cumin, chili powder, sea salt, and black pepper until evenly coated.
Heat the avocado oil in a large non-stick skillet over medium-high heat.
Add the seasoned steak, sliced red bell peppers, and red onions to the skillet.
Sauté for 5-6 minutes, stirring occasionally, until the steak is browned and the vegetables are tender-crisp.
Remove the steak and vegetable mixture from the pan and set aside; wipe the skillet clean with a paper towel.
In a small bowl, mash the avocado with lime juice and a pinch of salt to create a fresh guacamole.
Place the tortilla in the skillet over medium heat, sprinkle the cheese over one half, and top with the steak and vegetable mixture.
Fold the tortilla in half and cook for 2-3 minutes per side until the exterior is golden brown and the cheese is fully melted.
Slice the quesadilla into wedges and serve immediately with the prepared guacamole.