In a small bowl, whisk together the soy sauce, pineapple juice, brown sugar, ground cumin, and minced garlic. Place the steak in a sealable bag and pour in the marinade. Massage the marinade into the steak, then lay the bag flat in the refrigerator for at least 1 hour or overnight for best results.
In a medium bowl, combine the diced pineapple, chopped red bell pepper, diced red onion, diced jalapeno, and chopped fresh cilantro. Add the lime juice and lime zest. Mix well and set aside.
Preheat the grill to medium-high heat. Place the corn tortillas on the grill for about 30 seconds on each side, until warmed and slightly charred.
Remove the steak from the marinade and place it on the preheated grill. Grill for about 7-11 minutes, flipping occasionally, until a slight char is achieved on the outside and the steak reaches your desired level of doneness. According to the USDA’s rules they determine temperature doneness as 145 medium rare, 160 medium and 170 is well done, use a meat thermometer to cook to your desired temperature. Remove the steak from the grill and let it rest for at least 5 minutes. Thinly slice the steak against the grain into strips.
Place the grilled steak strips onto the corn tortillas. Top with the prepared pineapple salsa. Serve immediately and enjoy!