In a pan over medium heat, heat oil. Add tilapia and fry, turning once or twice, until golden and cooked through. Remove from pan and drain on paper towels.
In a pot over medium heat, add about 4 cups and bring to a boil. Add labong and cook for about 7 to 10 minutes or until tender. Drain labong and discard liquid.
In another pot over medium heat, combine 5 cups of water and onion. Bring to a boil.
In a bowl, combine bagoong with 1/2 cup of the boiling water. In a fine mesh strainer, strain bagoong to extract juice and discard small fish particles from the bagoong. Add the bagoong sauce into the pot. Lower heat to simmer.
Add the labong and continue to cook for about 3 to 5 minutes. Add fried fish and cook for another 3 to 5 minutes to slightly soften. Add saluyot leaves and continue to cook for about 2 to 4 minutes or until just wilted. Season with pepper to taste.