1. In non-reactive container, combine onion and lime juice. 2. Four hours before you plane to serve ceviche, combine ½ onion / lime juice mixture with tomato,     and citrus marinade. 3. Reserve the rest for garnish.  In saucepan, bring your water, and scallions to boil. 4. Reduce heat and simmer for 5 minutes.  Stir in shrimp, cover, and remove from heat.  5. Let shrimp steep for 2 minutes until pink. 6. Drain, and rinse under cold water.  Discard scallions. 7. In non reactive container, combine shrimp, marinade, and chopped cilantro.  Cover and refrigerate for 3 hours. 8. Adjust seasoning with Adobo, and add Goya Salsita, to taste. 9. Serve in individual bowls garnished with reserved onion / lime mixture, and sprigs of cilantro on the side.