01 -
Preheat the oven to 200°C. Prepare a 33x23 cm casserole dish by lightly greasing if not using an oven-safe pot.
02 -
Halve the chicken breasts lengthwise to create thinner cutlets. Pat dry and season both sides with salt, pepper, and Italian seasoning. Heat olive oil in a large pot over medium-high heat and sear chicken for 5–6 minutes per side until cooked through. Remove and let cool, then dice into bite-sized pieces.
03 -
Reduce heat to medium-low. Melt butter in the same pot, scraping up browned bits from the bottom for flavor. Add diced onion and cook for 4 minutes until softened. Stir in minced garlic and cook for 1 additional minute. Sprinkle flour over onion mixture, stirring to coat, and cook for 2 minutes to eliminate raw flour taste.
04 -
Gradually add chicken broth in small amounts, stirring between each addition to maintain a smooth texture. Add milk in a slow stream, whisking constantly until combined. Simmer sauce on low while preparing pasta.
05 -
Boil water separately and cook spaghetti according to package instructions until al dente. Drain and set aside.
06 -
Add softened cream cheese to the sauce, stirring continuously until fully melted and smooth. Let the sauce cool slightly, then gradually incorporate shredded cheddar cheese until melted and creamy. If needed, add a small amount of tomato juice to thin the sauce; otherwise, drain tomatoes well. Add diced tomatoes with green chilies and diced chicken into the sauce. Stir to combine.
07 -
Gently fold cooked spaghetti into the sauce mixture. If not using an oven-safe pot, transfer contents to the prepared casserole dish.
08 -
Top the surface with shredded mozzarella. Bake uncovered for 15 minutes until cheese is melted. For a golden top, broil at 245°C for 1–2 minutes, monitoring carefully to prevent burning.
09 -
Remove from oven. Sprinkle red pepper flakes and chopped fresh parsley to garnish before serving. Serve hot, accompanied by garlic bread if desired.