Bring a pot of water to boil over high heat and cook the penne pasta according to the direction on the box. Drain and set aside.

Meanwhile, in a dutch oven or large pot, heat the oil and 2 tablespoons of butter over medium high heat.

Toss the sliced chicken with the flour, cajun seasoning, salt and pepper in a bowl until well coated. Add the chicken to the oil and butter and let cook 1-2 minutes until browned and then flip it and let it cook on the other side for another 1-2 minutes. It doesn't need to be cooked all the way through.

Remove the chicken from the pot and set aside.

Add another tablespoon of butter to the pot, reduce the heat to medium and add the onions and bell peppers along with a pinch of salt. Cook. Stirring frequently until softened, about 5 minutes. Add the mushrooms, and garlic and let cook for 1 minute, stirring frequently.

Add the chicken broth and stir, scraping the bottom of the pot. Bring to a simmer and let cook for 3-4 minutes. Add the pasta, the chicken, and the cream and let cook until the chicken is cooked completely through. Season to taste and sprinkle the spinach on top. Serve immediately.