Preheat grill to medium-high (450°F). Pat steak dry and rub with 1 tbsp oil, salt, pepper, cumin, and paprika.
Toss peppers and onion with remaining oil and a pinch of salt. Use a grill basket if you have one.
Grill steak 3-4 minutes per side for medium-rare (internal 130–135°F). Remove and rest 5 minutes.
Grill vegetables 6-8 minutes, turning until charred and tender.
Slice steak thin against the grain. Warm tortillas on the grill 15–20 seconds per side.
Build fajitas with steak, peppers, onions, cilantro, and a squeeze of lime.