Prepare and drain spaghetti according to package directions.
Meanwhile, pour olive oil in a sauté pan over medium heat. Add onions, carrots, celery, and salt. Cook for 6 to 8 minutes, until onions have softened.
Add garlic, ground meat, oregano, and pepper. Cook for an additional 5 minutes, until the meat is browned and cooked through. Add the marinara sauce, stir, and bring to a simmer.
Add cooked spaghetti to meat sauce and toss to coat.