1. For the marinade, toast the cumin seeds in a small dry skillet over low heat until fragrant, 2 to 3 minutes, shaking the pan. Place the seeds in a small bowl and combine with the remaining marinade ingredients.
2. Trim the steaks of any excess fat, place them in a large zip-top plastic bag, and pour in the marinade. Seal the bag, squish everything around to coat the meat, and let marinate in the refrigerator for 8 to 12 hours, turning occasionally.
3. Combine the salsa ingredients in a medium bowl. For the best flavor, don’t do this more than 1 hour before you plan to serve it.
4. Remove the steaks from the bag and discard the marinade. Allow the steaks to stand at room temperature for 30 minutes before grilling.
5. Light a charcoal fire or preheat your gas grill on high. Oil the grill’s cooking surface.
6. Place the steaks on the grill and cook for 3 to 5 minutes total for medium-rare or to your desired degree of doneness, turning once. Remove to a cutting board and let rest for 2 to 3 minutes.
7. Meanwhile, divide the tortillas and wrap in two aluminum foil packets. Throw them on the grill until warmed through, about 2 minutes, turning once.
8. Cut the steaks into thin slices on the diagonal. Serve immediately on a platter with the warm tortillas and salsa in separate dishes and let your guests/family make their own.