Wash the chestnut pumpkin thoroughly, peel it, and cut it into bite-sized pieces.
Steam the chestnut pumpkin in a steamer for 15 minutes, then let it cool.
Place the steamed chestnut pumpkin in a bowl and mash it finely with a fork.
Season with salt and pepper. Finely chop cucumber and onion, then add them in.
Add olive oil and lemon juice, mix well, and serve on a plate.