Cut onion, garlic, and potatoes into small cubes. Heat oil in a pan over medium heat. Add onion, garlic, and mushrooms. Sauté for 2-3 minutes until softened. Deglaze the pan with vegetable broth. Add potato pieces and cook for 10 minutes.
Cut fish fillets into cubes and add to the pan along with carrot slices. Cook for 10 minutes. Stir in Cremefine and simmer for 1-2 minutes until the sauce is creamy.
Season with tomato paste, lemon juice, salt, and pepper to taste. Garnish with chopped parsley and chives.