Bring a large pot of water to a boil. Generously salt the boiling water, add the pasta and cook until al dente, 9-11 minutes; drain.
In the meantime, season cubed chicken with salt and pepper. In a large frying pan, heat olive oil. Saute chicken breasts until cooked through. Set aside.
In the same pan used for chicken breasts, melt the butter. Add the shallots and saute until soft, about 4 minutes.
Reduce the heat under the frying pan to low and add the stock, cheese, cream and lemon zest. Season with salt and pepper to taste and stir until all the ingredients are smooth and melted, about 4 minutes.
Add the pasta to the frying pan. Remove from the heat. Add the chicken and sage; toss briefly until the pasta is well coated with the sauce. If the sauce seems too thick, add a bit more chicken stock or a splash of hot water. Pour into a large, shallow bowl. Serve immediately.