In medium saucepot over medium-high heat, bring 2 cups water to boil; season with Adobo. Add shrimp. Remove pot from heat; cover tightly. Set pot aside until shrimp are pink, about 3 minutes. Drain shrimp and rinse under cold water until cool; set aside.
In large zip-top bag (or non-reactive container with lid), combine lemon juice, olive oil, 2 tbsp. cilantro, onions and jalapeño pepper; season with Adobo. Submerge shrimp in lemon mixture; seal bag and transfer to refrigerator. Chill until shrimp absorb flavor of marinade, at least 2 hours, or up to 24 hours.
To serve, remove shrimp from marinade, reserving ¼ cup marinade. Arranged cooked plantains on serving platter. Evenly divide shrimp among plantains; drizzle with reserved marinade. Sprinkle shrimp bites with avocado and remaining cilantro.