Boil rice in bags in salted water until half cooked (10 minutes). While the rice is cooking, peel the onion and garlic. Slice. Cut the mushrooms into small pieces.
Fry the onion in vegetable oil for 2-3 minutes, add the mushrooms and simmer until the liquid has evaporated. Add spinach to the mushrooms and remove from heat after half a minute, mix. In a heat-resistant casserole dish, grease with vegetable oil, put one bag of rice. Then lay out a layer of minced chicken, salt and pepper. Spread the mushroom filling over the chicken layer. Top with a layer of rice from the second bag.
Prepare filling: for this 1 tbsp. l. fry flour in butter, add milk, bring to a boil, add grated cheese and cook over low heat until thickened, 1-2 minutes. Cook in an oven preheated to 200 degrees for 45 minutes.