Preheat the oven to 400 degrees F. Line a large baking sheet with foil and lightly spray the foil with olive oil cooking spray.
Add all meatball ingredients (except marinara sauce) to a large bowl and use your hands to combine. Scoop the meat mixture into 3-tablespoon-sized balls and arrange them on the prepared baking sheet. You should get about 24 meatballs.
Bake the meatballs until they are cooked through (ground beef should be cooked to an internal temperature of 160 degrees F, which you can check with an instant-read thermometer), about 15 to 20 minutes. If you want to brown the tops, broil the meatballs briefly after baking. Add the meatballs to a large bowl and toss with 1 jar of warmed marinara sauce.
ASSEMBLE THE SPAGHETTI AND MEATBALLS:
Toss the cooked spaghetti with ½ jar of warmed marinara sauce. Place the meatballs on top of the spaghetti, and serve along with the remaining ½ jar of marinara sauce to spoon on top, if desired.
Serve with fresh basil leaves and freshly grated parmesan cheese for topping.