Boil a large, salted pot of water for the pasta. Cook your pasta according to package directions until al dente.
Meanwhile, cut the chicken into bite-size pieces and sprinkle them with garlic powder, then coat them in flour.
Add the olive oil and 1 tablespoon of the butter to a skillet over medium-high heat.
Once the skillet is hot, add the chicken. Cook it for about 5 minutes, turning with tongs, until the chicken is slightly browned (it'll finish cooking later so don't overcook). Transfer the chicken to a plate.
Add the remaining butter to the skillet. Add the mushrooms and cook for 3-4 minutes or until the mushrooms have released water and it's cooked off a bit. Take the mushrooms out of the pan (ok to put on same plate as the chicken).
Add the chicken broth, marsala, and Dijon mustard to the pan. Stir/whisk until the mustard has dissolved and let it bubble for 2 minutes or so (it should reduce a bit).
Add the cream, chicken, and mushrooms to the pan, and reduce the heat to medium. Cook for a few minutes until the sauce has thickened and the chicken has cooked through.
Season with salt & pepper as needed. Drain the pasta and toss it with the sauce (add a little water from the pasta if needed to thin the sauce) and serve with parmesan cheese if using.