In a medium bowl, combine the lean ground beef with sea salt, black pepper, and dried oregano until well incorporated.
Form the beef mixture into 8 small, uniform meatballs.
Heat the olive oil in a non-stick skillet over medium heat.
Add the meatballs to the skillet and brown on all sides for about 5-6 minutes until a golden crust forms.
Remove the meatballs from the pan and set aside on a plate.
In the same skillet, add the finely diced onion and minced garlic, sautéing for 2-3 minutes until translucent and fragrant.
Pour in the tomato puree and bring to a gentle simmer, scraping any browned bits from the bottom of the pan.
Return the meatballs to the skillet, cover with a lid, and cook for another 5 minutes to ensure they are cooked through.
Stir in the fresh spinach until just wilted and garnish with chopped fresh basil before serving.