In a large pot, bring water to boil, season water with salt, and add in your pasta.
In a skillet, saute the chicken with some vegetable oil on medium high heat until sides are browned and chicken is cooked through. Set aside.
In the same skillet, saute the onions and mushrooms until tender. Add the chicken back into the skillet and add in the spinach as well. When it has wilted down, add the mascarpone cheese, stir until melted and well combined.
Your pasta should be done at this point, or close to being done. Drain the pasta well and add it to the skillet. Stir to coat the pasta in the cream sauce.