Peel and boil the potatoes in water together with the bouillon cubes. Drain and mash. Meanwhile, place the fish in boiling water and cook for a few minutes until cooked. Remove the fish and place the peas in the same water for a few minutes. Drain the peas and flake the fish with a fork. Mix the 3 ingredients together adding a bit of salt. Form about 25 small balls.
Place the flour, egg and breadcrumbs in 3 separate plates. Add the vegetable powder to the breadcrumbs and mix. Roll each ball in a bit of flour, then dip it in the egg and then coat with the breadcrumbs. Repeat with all remaining balls. Chill in the fridge for 30 minutes.
In a large frying pan, heat some oil (about 1cm) and shallow fry the croquettes for 3 minutes, turning continuously until crispy and golden brown on all sides. With a slotted spoon, transfer the croquettes to a plate lined with kitchen paper and let them rest for a few minutes before serving.
Note: This can be regarded as a full meal as it contains fish, potato and vegetable, so no side dish is needed!