In a large saucepan, boil the shrimp in water for 3 minutes, until pink. Drain and pour cold water over the shrimp to stop cooking. After a minute, take the shrimp out of the water with a slotted spoon and transfer to a plate, set aside.
In a cast-iron saucepan, heat oil over medium heat, pour mushrooms, onion, garlic and 1/4 teaspoon of salt into the saucepan, fry, stirring occasionally, for about 5 minutes, until the vegetables are soft. Transfer the contents of the pot to a plate, cover with foil to keep the vegetables warm.
Pour the barley into the saucepan in which the vegetables were cooked and fry, stirring occasionally, for about 1 minute. Pour in the wine and the remaining 1/4 teaspoon of salt, cook, stirring occasionally, for about 4 minutes. Then gradually add the broth (1/2 cup at a time) and mix well after each serving, allowing the liquid to evaporate completely. Add boiled shrimp, mushroom mixture, spinach, cheese, lemon juice, and pepper, mix well and serve immediately.