Slice the flank steak against the grain into very thin strips.
In a small bowl, combine the chili powder, cumin, garlic powder, and sea salt.
Toss the steak strips with the spice blend until evenly coated.
Heat the avocado oil in a large skillet over medium-high heat.
Add the sliced red and green bell peppers to the skillet and sauté for 3-4 minutes until tender-crisp, then remove them from the pan.
In the same skillet, add the steak strips in a single layer and sear for 2 minutes per side until well-browned.
Drizzle the lime juice over the steak and toss to deglaze the pan, then remove the steak from the heat.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle the shredded cheddar cheese over half of the tortilla, then top with the steak and sautéed peppers.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is crispy golden-brown and the cheese is melted.
Slice the quesadilla into wedges and garnish with chopped fresh cilantro before serving.