• Step 1: Preheat your oven to 375°F (190°C). Cook the spaghetti or linguine according to the package instructions, drain, and set aside.
• Step 2: In a large skillet, heat the olive oil over medium-high heat. Add the cubed chicken and sauté until it’s cooked through, about 6-8 minutes. Remove the chicken from the skillet and set it aside.
• Step 3: In the same skillet, sauté the onion and garlic until they’re fragrant and the onion is translucent, about 3-4 minutes. Add the sliced mushrooms and cook for an additional 2-3 minutes.
• Step 4: In a large bowl, combine the cooked spaghetti, chicken, and the mushroom mixture. Stir in the cream of mushroom soup and milk until well blended.
• Step 5: Transfer the mixture to a 9×13 inch baking dish. Sprinkle the top with the cheddar and Parmesan cheeses, followed by the panko breadcrumbs. Drizzle the melted butter over the breadcrumbs.
• Step 6: Bake the chicken tetrazzini for 25-30 minutes, or until the top is golden brown and the cheese is melted and bubbly. Allow the dish to cool for 5-10 minutes before serving.