Run the cooked noodles under cold water & stir them to prevent them from sticking while you make the sauce.
In a large skillet over medium low heat, melt the butter. Once melted add in the onions. Sprinkle them with the garlic powder, and then stir them to combine.
Cook, stirring occasionally, until the onions are soft.
Pour in the broth, and using a sturdy spoon scrape the bottom of the skillet to get up any of the delicious browned bits. Let the mixture simmer for 1-2 minutes.
Slowly pour the cream and half & half into the pan, stirring in as you do. Once smooth add the Cajun seasoning, lemon juice, salt & pepper- stirring to combine.
Bring the sauce to a boil, and then reduce the heat to low. Stir in the cheese until melted & the mixture's smooth.
Let the sauce simmer for 10 minutes, or until slightly thickened. Remember to stir often.
Add the noodles to the skillet (assuming there's room, otherwise use a large pot), and gently toss them with the sauce until everything's good and coated.