Peel and chop the onions. Heat the oil in a frying pan. Fry the onions in it until they are transparent. Pour in broth. Add the barley and cook on medium heat for about 25 minutes.
In the meantime, clean and peel the carrots and cut them into diagonal slices. Add the carrots to the barley about 10 minutes before the end of the cooking time. Remove the skin of the mackerel and cut the fillets into large pieces. Wash parsley, shake dry.
Pluck off leaves and chop finely.
Add the frozen peas to the stew about 3 minutes before the end of the cooking time and finish cooking. Add about 2/3 parsley to the soup. Season to taste with salt, pepper and cumin. Arrange the soup, carefully fold in the mackerel pieces and sprinkle with the remaining parsley.