In a large bowl, combine ground beef, breadcrumbs, grated Parmesan cheese, egg, minced garlic, chopped parsley, dried oregano, salt, and black pepper. Mix gently until just combined.
Shape the mixture into 24 evenly sized meatballs, about 1 inch in diameter.
Heat olive oil in a large skillet over medium heat. Add meatballs in batches, cooking until browned on all sides, about 5 minutes per batch. Remove browned meatballs and set aside.
In the same skillet, add chopped onion and sauté until translucent, about 5 minutes.
Add crushed tomatoes, sugar, dried basil, and dried thyme to the skillet. Stir to combine and bring the sauce to a simmer.
Return the browned meatballs to the skillet, cover, and simmer gently for 20 minutes until meatballs are cooked through and sauce has thickened.
Meanwhile, bring a large pot of salted water to a boil. Add spaghetti and cook according to package instructions until al dente, about 8-10 minutes.
Drain pasta and toss with a small amount of the tomato sauce to prevent sticking.
To serve immediately, plate pasta topped with meatballs and sauce. To make ahead, allow meatballs and sauce to cool completely, then store in an airtight container in the refrigerator for up to 3 days or freeze for up to 3 months.
Reheat meatballs and sauce gently on the stovetop over low heat until warmed through before serving with reheated pasta.