Answer:
I believe it is B
Explanation:
In all sense, they are all correct, but it sounds weird, so we can take off A and C. Now B) Loaded with mushrooms and peppers, Clara served homemade spaghetti to her parents and grandparents. This sounds grammatically correct due to the comma, and it is not a very long sentence that seems awkward.
Now C) Clara served homemade spaghetti loaded with mushrooms and peppers to her parents and grandparents. I'd like to say that this is a sentence that can be split in two. Clara made homemade spaghetti loaded with mushrooms and peppers. She served it to her parents and grandparents.