Slice the top sirloin into very thin strips across the grain for maximum tenderness.
In a small bowl, whisk together the chili powder, cumin, garlic powder, sea salt, black pepper, and lime juice to create a marinade.
Toss the steak strips in the marinade until evenly coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the thinly sliced red bell peppers and onions to the skillet, sautéing for 3-4 minutes until they are tender-crisp and slightly charred.
Remove the vegetables from the pan and set aside.
Add the steak to the same hot skillet in a single layer, searing for 1-2 minutes per side until a brown crust forms.
Wipe the skillet clean and place the almond flour tortilla in the center over medium heat.
Sprinkle half of the shredded cheddar on one side of the tortilla, then layer on the steak, sautéed vegetables, and fresh cilantro.
Top with the remaining cheese and fold the tortilla in half.
Press down with a spatula and cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.