Preheat oven to 375 degrees F with rack in center of oven.

Spray a 9x13x3-inch deep casserole dish with kitchen pan spray and set aside.

Bring a large pot of water to a boil and salt with a teaspoon or so of kosher salt. Add spaghetti and boil four minutes less than box directions. Our box of Barilla thick spaghetti cooking directions states to boil 11 minutes. We boiled for seven minutes. Drain, rinse with cold water and set aside.

In a large saute pan, add 2 tablespoons of the olive oil and over medium high heat, saute the mushrooms for eight minutes, stirring often.

Keep the burner on medium high and push the mushrooms to the edge of the pan. Add the remaining tablespoon of oil then add the onions and pepper and cook three minutes, stirring into the mushrooms as they cook.

Add the garlic and cook one minute more then remove the pan from heat.

While vegetables are sautéing, place empty pasta pot back on the stove and over medium heat, melt the butter. Once melted, stir in the flour and cook for three minutes, stirring often with a wooden spoon.

Whisk in the heated chicken stock a little at a time to get a smooth sauce.

Whisk in the heavy cream and heat the sauce to hot.

Add the cream cheese and whisk until it melts into the sauce.

Season the sauce with the salt, white pepper and nutmeg, then remove from heat.

Add the drained canned tomatoes to the pot with the sauce along with the partially cooked spaghetti, sautéed peppers and onions mixture, cooked chicken and half of each of the cheddar and Jack cheeses.

Use tongs and a large firm rubber spatula and toss the mixture to combine.

Pour into the prepared baking dish and top with the remaining cheddar and Jack cheese and bake for 40 minutes uncovered.

Place under the broiler to brown the top then remove from the oven and let rest for 15 minutes.

As it rests, it firms up which will allow you to cut 3×4 into 12 neat even portions. Remove portions with a flexible rubber spatula and serve.