Heat oil in large, non-stick skillet over medium-high heat. Add onions and pepper. Cook, stirring occasionally, until vegetables soften but do not brown, 8-10 minutes. Add 2 tbsp. cilantro, garlic, 1 tsp. Adobo and Sazón. Cook, stirring, until garlic is fragrant, about 1 minute more. Add tomatoes to skillet. Cook, stirring occasionally, until moisture from tomatoes evaporates and mixture begins to thicken, about 5 minutes. Transfer sofrito mixture to non-reactive container; chill until cold. Scoop out and reserve 6 tbsp. sofrito mixture; mix with remaining cilantro. Cover and reserve in refrigerator.
Add pork steaks to container with remaining sofrito; massage to coat completely in sauce. Cover with plastic wrap. Transfer pork to refrigerator. Marinate at least 4 hours, or up to 48 hours. Bring pork to room temperature 30 minutes before cooking.
Heat grill to medium-high heat. Remove pork from sofrito mixture, shaking off excess. Add pork to hot-greased grill grates. Season pork with Adobo, if desired. Cook, flipping once, until pork is dark golden brown and cooked through (internal temperature of at least 140 °F), 17-20 minutes. Transfer pork to platter. Top with reserved sofrito mixture. Serve