Begin by having all of your ingredients prepared and cooked ahead of time. That means your chicken and your pasta. The other ingredients should be prepared as well. You can prepare all of your vegetables and dicing while the pasta and chicken are cooking.

Preheat your oven to 350 degrees.

Bring a skillet to medium-high heat. Add in the olive oil, then toss in the peppers, onions, spinach, and garlic. You only want to cook for a few minutes to sweat the onions and garlic, and slightly wilt the spinach. After a few minutes, remove the skillet from the stove.

To a sauce pan, add the butter, and let it completely melt. Medium heat is fine on this. Next, add in the flour, and incorporate this into the butter, mixing with a wooden spoon for about 3 minutes. It will begin to turn a nutty brown color. This is good. Slowly add in the half and half, then the milk. Raise the heat a bit, and continue stirring for about 5 minutes, if not longer, until the sauce begins to thicken.

Season the sauce with the salt, pepper, and Old Bay, and give a good stir. Add in the cheese. Stir, then remove the sauce pan from the heat.

To a large mixing bowl, add in the pasta, chopped onion, spinach, garlic, chicken, kielbasa, cheese, and peppers. Give a good stir, then pour in the sauce. Continue to stir until all of your ingredients are nicely coated with the cheese sauce.

Pour this mixture into a large casserole dish and place in the oven for 25 minutes, or until the cheese is nice and bubbly.