Prepare the mushrooms for julienne. Chop them finely. Chop the onion and garlic. Heat a frying pan with olive oil, fry the onion, then add the mushrooms. Add salt, pepper and fry until the mushrooms are ready.
Cut the boiled chicken fillet and put it in the pan with the mushrooms. Simmer for 2-3 minutes, add sour cream and chopped garlic. Simmer for a few seconds until the mixture boils, and remove from the stove.
Grate the cheese. Transfer the julienne into baking or cocotte dishes. Sprinkle the grated cheese on top of the julienne.
Place the dish in the oven to bake for 10 minutes. Serve the julienne to the table.