Cook the lentils separately in salted water until lightly al dente (the lentils have different cooking times) and drain. Clean the vegetables and cut them into fine cubes. Sauté the shallot, garlic and the vegetable cubes in a little butter. Add the lentils and season with salt and pepper. Extinguish with vegetable soup and stir in balsamic vinegar. Simmer gently for about 5 minutes.
Finally, stir in the remaining butter and season with salt and pepper and sugar. Sprinkle with chopped parsley.
Season the catfish fillet with salt and pepper and roast in a frying pan with olive oil for 2-3 min on each side.
Arrange the fillets on the colored lentils and drizzle with the juice of a lemon, if desired.