Bring water to boil with salt. Cook pasta according to package instructions.
Cut chicken breast into smaller bite-size pieces.
Heat up a skillet with the olive oil and add chicken.
Season chicken with salt and black pepper and cook on all sides.
Take chicken from the skillet and keep it aside for later. Bring skillet back to the heat and add butter.
Stir all-purpose flour into the butter over a medium to slow heat setting and mix in.
Quickly continue to pour in some of the milk and whisk it into the flour-butter mixture. Continue to whisk and to do that until you used up all the milk, and the sauce is looking smooth without pieces.
Takedown the heat to a low flame. Stir in salt, black pepper, onion powder, garlic powder, Italian seasoning (or oregano), and dijon mustard. Combine and allow the sauce to thicken.
Stir in cheese and cooked chicken from earlier. Combine to a cheesy chicken sauce.
Heat up oven to 350° Fahrenheit/ 180° Celsius.
Place cooked pasta into the baking dish and pour chicken white sauce over the paste. Spread and mix the sauce into pasta.
Top it all with grated cheese.
Bake uncovered at 350° Fahrenheit/ 180° Celsius for about 20 minutes or until it looks golden crispy baked.
Dijon mustard is optional but I recommend that you add it. It's my secret ingredient. It adds flavor and mustard helps to bind the sauce further too.