Halve the pineapples lengthwise and carefully scoop out the flesh with a serrated knife. Dice the flesh into small cubes over a bowl to capture the juice. Reserve the shells for serving.
Peel the avocados and cut the flesh into strips, tossing with lemon juice to prevent browning. Rinse and pat dry the cherry tomatoes, then halve them. Slice the hearts of palm. Fill the pineapple shells with avocado strips, tomato halves, palm slices, pineapple cubes, and shelled prawns.
For the vinaigrette, whisk sunflower oil, lime juice, reserved pineapple juice, salt, and pepper. Add a few drops of Tabasco and a pinch of cayenne.
Drizzle the vinaigrette over the filled pineapples. Garnish with chopped chervil chives and top each with a pink prawn. Serve chilled for a refreshing tropical starter.
