Peel and wash the carrots and cut them into thin sticks. Peel and finely chop the onion. Prepare rice in boiling salted water according to package instructions. Wash fish, cut into pieces and sprinkle with 2 tablespoons of lemon juice.
Dab fish dry, season with salt and pepper. Heat oil in a pan. Sauté the fish for 5 minutes and take it out. Sauté the carrots and onions in the frying oil. Deglaze with stock and milk and bring to the boil.
Add peas and cook for 4 minutes. Stir in the sauce thickener, bring to the boil again. Season to taste with salt, pepper and remaining lemon juice. Wash the dill and chop finely, except for a little garnish. Add the dill and fish to the sauce and leave to stand for about 3 minutes.
Pour the rice onto a sieve. Arrange rice and fish ragout on plates. Serve garnished with dill and lemon slices.