In batches, cook the ground beef in a large skillet over medium-high heat until browned and no longer pink. Once cooked, drain excess fat from the meat. Set the cooked beef aside.

In the same skillet, add the diced onions and sauté over medium heat until they become translucent and soft. This should take about 5-7 minutes. Set aside when done.

Generously coat the inside of a large roaster pan with non-stick cooking spray to prevent sticking. Pour the tomato juice and pasta sauce into the prepared pan. Set the roaster to 300℉ to begin heating the mixture.

Sprinkle the kosher salt, black pepper, garlic powder, and dry mustard evenly over the liquid in the roaster. Stir well to combine all the seasonings. I like to stir thoroughly at this point to ensure the spices are evenly distributed throughout the sauce.

Add the cooked ground beef from Step 1 and the sautéed onions from Step 2 into the roaster pan with the seasoned sauce. Stir everything together thoroughly, then cover and cook at 300℉ for 1½ hours, stirring every 30 minutes to prevent sticking.

Break the dry spaghetti into smaller pieces and add it into the roaster pan over the sauce mixture. Stir well so the pasta is thoroughly coated and submerged in the liquid. Cook uncovered for an additional 45 minutes to 1 hour, stirring every 15 minutes, until the pasta is tender.

Once the spaghetti is cooked to your liking, reduce the roaster to warm or the lowest temperature setting to keep the dish hot while serving. Stir often to prevent sticking or drying out.