Combine the pineapple juice, soy sauce, brown sugar, olive oil, sesame oil, minced ginger, minced garlic, and sriracha together in a large ziplock bag; seal and mix well.
Add the flanken short ribs to the marinade in the ziplock bag and toss to coat evenly. Refrigerate for 1-24 hours (I marinated for about 12 hours).
Remove the meat from the refrigerator 30 minutes prior to cooking.
Remove the short ribs from the marinade and season them with sea salt and freshly cracked pepper, to taste.
Heat a grill pan over medium-high heat. Coat with cooking spray then lay a few of the short ribs in the HOT grill pan and cook for 3-4 minutes then flip and continue to cook for another 2-3 minutes, or until cooked to your desired degree of doneness. Remove from the pan and set aside on a serving plate with a loose tin foil tent. Finish cooking the remaining short ribs. Side Note: My flanken short ribs were thicker than normal. If yours are quite thin, cook for less time.
Serve the teriyaki flanken short ribs topped with chopped cilantro and toasted sesame seeds. Enjoy.