Preheat your oven to 375°F. Slice each chicken breast in half horizontally to make four thin cutlets.

Heat olive oil in a large skillet over medium heat. Add the chicken cutlets and cook for 7–10 minutes, flipping halfway through, until cooked through and golden on both sides. Set aside to rest, then chop into bite-sized pieces.

While the chicken cooks, bring a large pot of salted water to a boil. Add spaghetti and cook until al dente. Drain and set aside.

In the same skillet used for the chicken, melt the butter over medium heat. Add diced onion and minced garlic, and sauté for 3–4 minutes until the onion softens.

Sprinkle in the flour and stir to coat the onion and garlic. Cook for 2–3 minutes to remove the raw flour taste.

Gradually add the chicken broth while stirring to deglaze the pan and create a smooth sauce. Bring to a simmer.

Add salt, pepper, Italian seasoning, ½ cup of cheddar, ½ cup of mozzarella, and the heavy cream. Stir until the cheese melts and the sauce is smooth and thick.

Add the drained tomatoes, chopped chicken, and cooked spaghetti to the skillet. Stir until everything is evenly coated with the sauce.

Transfer the mixture to a 9×13-inch baking dish. Top with the remaining cheddar and mozzarella.

Bake uncovered for 25 minutes, or until the cheese is melted and the edges are bubbling.