1.1. Sprinkle each side of the steak with a liberal coating of salt and pepper followed by 1 tablespoon lime juice (2 tablespoons in total). Heat the oil in a heavy-bottomed 12-inch skillet over medium-high heat until smoking. Lay the steak in the pan and cook, without moving, until well browned, 4 to 5 minutes. Using tongs, flip the steak. Reduce the heat to medium. Continue to cook until the second side is browned, 4 to 5 minutes. Transfer the steak to a plate, drizzle with the remaining 2 tablespoons lime juice, tent loosely with aluminum foil, and let rest for 10 minutes.

2.2. Meanwhile, return the skillet to medium-high heat and add the bell peppers, onion, cumin seeds, 1/2 teaspoon salt, and 2 tablespoons water. Cook, stirring occasionally and scraping the bottom of the skillet to release any browned bits, until the onion is very soft and browned, 5 to 6 minutes. Transfer the vegetables to a serving bowl and adjust the seasonings with salt and pepper to taste.

3.3. Heat a large nonstick skillet over medium heat for 2 minutes and lightly toast each tortilla in the pan for 10 to 15 seconds per side. Stack the toasted tortillas in a clean towel and wrap to keep warm.

4.4. TO SERVE: Slice the steak very thinly against the grain and place the meat in a serving bowl. Pour any released juices over the vegetables. Serve the vegetables, meat, and tortillas along with bowls of salsa, sour cream, and avocado so diners can assemble their own fajitas.