Mix torn gluten free bread and grated onion in a large mixing bowl then let sit and soften for a minute. Add egg, garlic, dried parsley, salt, and pepper then stir to combine. Crumble ground beef over mixture then use your hands to mix until just combined - don't over mix. Shape into golf ball sized meatballs (about 18-20) then place onto a plate.
Add enough extra virgin olive oil to cover the bottom of a large, heavy-bottomed skillet that's at least 10" (cast iron preferred) then heat over medium/medium-high heat (6/10 on the heat scale). Add half the meatballs then saute until evenly browned on all sides but not completely cooked through, carefully turning the meatballs with tongs or a spoon as they will be very soft. Transfer browned meatballs to a plate. Brown second batch of meatballs then gently add the first batch back into the skillet. Remove skillet from heat to cool down for a few minutes.
After the skillet has slightly cooled, carefully add marinara sauce then use a spoon to gently coat all the meatballs in the sauce. Return skillet over medium-low heat then simmer until meatballs are cooked through, 15-20 minutes, basting and gently turning meatballs over with a spoon every so often. If the meatballs are taking too long to cook, place a lid on top of the skillet, or crimp a piece of foil on top of the skillet, and simmer until cooked through. If sauce gets too thick while simmering, add a generous glug of chicken broth.
Meanwhile, bring a large pot of water to a boil, season with salt, add pasta, then cook according to package directions. Drain pasta then serve with meatballs and sauce.
Notes
I like Canyon Bakehouse Mountain White bread (crust removed first) in this recipe but really any gluten free sandwich bread will work. Remove crusts first.