In a Dutch oven over medium heat, sauté the diced onion in oil until softened (~3-4 min). Add ground beef, salt & pepper, and cook until nicely browned. Drain excess fat.
Add crushed tomatoes, sugar, and beef broth. If using Parmesan rind, add now. Bring to a boil.
Add frozen mixed vegetables. Reduce to a simmer and cook ~10 minutes.
Add orzo. Continue to simmer ~8-10 minutes, stirring occasionally, until pasta is tender. Remove Parmesan rind if used.
Taste and adjust salt and pepper. Serve hot with plenty of grated cheese and crusty bread & butter.