In small bowl, mix together 1 ½ tbsp. olive oil, 1 tbsp. garlic, Sazón and 1 tsp. Adobo until combined. Rub spice mixture all over ribs. Place ribs in large roasting pan, meaty side-up; cover with plastic wrap. Marinate, chilled, at least 4 hours, and up to 24 hours for best results.
Heat oven to 350°F. Remove ribs from refrigerator; remove and discard plastic wrap. Pour 2 cups water in roasting pan. Cover pan tightly with foil. Cook, covered, until ribs are tender, about 2 hours. Remove pan from oven; transfer ribs to platter.
Meanwhile, heat remaining ½ tbsp. olive oil in medium pot over medium-high heat. Add onions and remaining 1 tbsp. garlic. Cook, stirring occasionally, until onions are soft and translucent, about 5 minutes. Stir in ¾ cup water, tamarind pulp, brown sugar, soy sauce, pepper flakes and remaining 1 tsp. Adobo; bring to boil, stirring occasionally. Reduce heat to medium. Cook, stirring occasionally, until mixture thickens and reduces to 1 cup, about 15 minutes; chill.
Heat grill to medium-high heat. Using pastry brush, brush ribs all over with glaze. Place ribs, meaty-side down, on hot, greased grill grates. Cook, flipping and brushing with glaze, until ribs are heated through and develop dark golden brown grill marks, about 5 minutes. Transfer ribs to serving platter; brush with more glaze before serving.