Peel the mango, cut the flesh off the stone. Puree mango and lemon juice. Cut passion fruit in half, scrape out the flesh and stir in. Season to taste with salt and pepper.
Wash the cucumber, halve lengthwise, remove seeds and grate coarsely. Mix half with yoghurt. Season to taste with salt and pepper. Season the rest of the cucumber with a little salt. Put aside.
Rinse fish, pat dry and cut into pieces. Fry in hot oil for 2-3 minutes on each side. Season with salt and pepper. Arrange on the yoghurt. Cut cress from the bed and sprinkle with the rest of the cucumber.
Drizzle with dressing.