Preheat your oven to 400°F and line a baking sheet with parchment paper.
In a large bowl, combine the ground beef, egg, finely diced yellow onion, minced garlic, dried oregano, sea salt, and black pepper.
Gently mix the ingredients by hand until just combined, being careful not to overwork the meat.
Roll the mixture into approximately 6-8 evenly sized meatballs and place them on the prepared baking sheet.
Bake for 15-18 minutes until the meatballs are cooked through and slightly browned.
While the meatballs bake, warm the marinara sauce in a small saucepan over medium-low heat.
In a separate skillet, heat the olive oil over medium heat and quickly sauté the zucchini noodles for 2-3 minutes until just tender.
Toss the cooked meatballs in the warm marinara sauce and serve immediately over the zucchini noodles.