For the fish-rhubarb curry, rinse the fish fillets, pat dry, cut into bite-sized cubes and marinate with lemon juice, salt and pepper.
Roughly chop the onions. Finely chop garlic. Peel rhubarb and cut into pieces about 1 cm. Heat oil and sauté onions until translucent.
Add garlic, rhubarb, curry powder and sugar and sauté briefly. Add soup and soy sauce and simmer for about 10 minutes.
Add fish cubes to the sauce and let simmer on low heat for about 3 minutes. Season to taste and serve sprinkled with parsley.