Slice the sirloin steak into very thin strips against the grain.
In a small bowl, whisk together the nutritional yeast, smoked paprika, chili powder, cumin, garlic powder, and sea salt.
Toss the steak strips in the spice mixture until evenly coated.
Heat avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the steak to the pan and sear for 2-3 minutes until browned and caramelized; remove steak from the pan and set aside.
In the same pan, add the sliced bell peppers and onions, sautéing for 3-4 minutes until tender-crisp with slight char marks.
Return the steak to the pan and toss with the vegetables for 1 minute to meld the flavors.
Warm the low carb tortillas in a dry skillet for 30 seconds per side until pliable and toasted.
Divide the steak stir-fry evenly between the two tortillas.
Drizzle with warm queso cheese and top with a dollop of sour cream and fresh salsa.