Slice the chicken breasts in half lengthwise to create thinner cutlets.

Pat dry and season with Italian seasoning, salt, and pepper.

Heat olive oil in a large skillet over medium-high heat.

Sear the chicken for 5–6 minutes per side, until cooked through.

Remove from the skillet and let rest. Dice into bite-sized pieces.

Reduce heat to medium-low. Melt the butter in the same skillet, scraping up any browned bits from the bottom.

Add the diced onion and cook for about 4 minutes, until softened.

Stir in the garlic and cook for 1 minute.

Sprinkle the flour over the onions and stir to coat. Cook for 2 minutes.

Gradually add the chicken broth, stirring continuously until smooth.

Slowly add the milk, whisking until fully combined.

Add the softened cream cheese and stir until melted and smooth.

Reduce heat to low and stir in the shredded Colby cheese until melted.

Stir in the tomato sauce.

Bring a large pot of salted water to a boil.

Cook the thin spaghetti according to package directions until al dente.

Drain the pasta.

Add the cooked chicken and spaghetti to the sauce.

Toss until everything is evenly coated.

Garnish with chopped parsley and serve warm.