In a large skillet, heat the olive oil over medium-high heat. Add the shallot, garlic and crushed red pepper; cook until the shallot is softened, 2 to 3 minutes. Add the barley and cook, stirring, for 1 minute. Add the wine and cook until most of the liquid is absorbed, about 2 minutes. Add the chicken broth, 1 1/2 cups water and 1/2 teaspoon each salt and black pepper; bring to a boil. Lower the heat and simmer, covered, until the grains are tender but chewy, about 30 minutes.
Stir in the spinach, mascarpone, grated parmigiano-reggiano and grated lemon peel; season with salt and black pepper. Serve immediately, sprinkled with the thinly sliced lemon peel and shaved parmigiano-reggiano.