In a bowl, mix together olive oil, lime juice, minced garlic, cumin, chili powder, salt, and black pepper. Add flank steak to the marinade, ensuring it is well coated. Cover and refrigerate for at least 1 hour, or overnight for best results.

Grill the Steak

Preheat the grill to medium-high heat. Remove the steak from the marinade and grill for 5-7 minutes on each side or until it reaches your desired doneness. Let the steak rest for a few minutes before slicing it thinly against the grain.

Prepare the Serrano Slaw

In a large bowl, combine shredded cabbage, sliced serrano peppers, diced roasted poblano, and chopped cilantro. Toss with a pinch of salt and a splash of lime juice to taste.

Make the Chimichurri Mayo

In a small bowl, mix together mayonnaise and chimichurri sauce until well combined.

Assemble the Sandwich

On each sandwich roll, spread a generous amount of chimichurri mayo, layer with sliced steak, add a handful of serrano slaw, top with French fried onions, and finish with pico de gallo. Close the sandwich and serve immediately.