Thinly slice the beef sirloin into bite-sized strips and pat dry with a paper towel.
In a small bowl, combine the chili powder, cumin, garlic powder, sea salt, and black pepper; toss the steak strips in the spice blend until evenly coated.
Heat the avocado oil in a large non-stick skillet over medium-high heat.
Add the steak to the skillet and sear for 2-3 minutes until browned and cooked to your preference, then remove from the pan and set aside.
In the same skillet, add the sliced bell peppers and red onions, sautéing for 3-5 minutes until they are tender and have developed a light char.
Wipe the skillet clean and return it to medium heat.
Place the tortilla in the skillet, sprinkling half of the shredded cheddar on one side.
Layer the cooked steak and sautéed vegetables over the cheese, then top with the remaining cheddar.
Fold the tortilla in half and cook for 2 minutes per side until the shell is golden brown and the cheese is completely melted.
Remove from the heat, drizzle with fresh lime juice, and slice into three wedges before serving.