How to Make It
Heat oven to 425° F. Toss the carrots, lemon juice, olive oil, sesame seeds, cumin, and ¼ teaspoon each salt and pepper on a large rimmed baking sheet. Roast until tender and browned, 20 to 25 minutes, tossing halfway through.
Meanwhile, heat a large cast-iron skillet over medium-high heat. Season the steak with ¼ teaspoon each salt and pepper. Cook until an instant-read thermometer inserted into the thickest steak registers 125° F, 3 minutes per side for medium-rare. Let rest for 5 minutes before slicing across the grain.
Top the tortillas with the carrots, steak, and avocado, dividing evenly. Serve topped with the watercress and sour cream, with the lemon wedges alongside.