In a large bowl, whisk together all marinade ingredients until combined.
Add the pre-sliced steak to the marinade and toss until fully coated. Cover and refrigerate for at least 30 minutes, or up to 6 hours.
Preheat a cast iron skillet over medium-high heat.
Add the marinated steak to the hot skillet in a single layer, working in batches if needed. Cook quickly until just cooked through and lightly caramelized.
Toast the flour tortillas over a gas flame or in a dry skillet until lightly charred on both sides.
Assemble the tacos by adding steak to each tortilla and topping with slaw, guacamole, diced tomatoes, and a squeeze of fresh citrus. Serve immediately.