1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
2. In a large bowl, combine the ground beef, chopped spinach, minced garlic, breadcrumbs, Parmesan cheese, beaten egg, salt, pepper, and oregano. Mix gently until all ingredients are well incorporated.
3. Take a small amount of the meat mixture and flatten it into a disc in your hand. Place a cube of mozzarella in the center and fold the meat around it, forming a ball. Make sure the cheese is completely covered to avoid leakage during baking.
4. Heat olive oil in a skillet over medium heat. Add the meatballs in batches, browning them on all sides. This should take about 5 minutes per batch.
5. Transfer the browned meatballs to the prepared baking sheet. Bake in the preheated oven for 15-20 minutes, until cooked through and the cheese is melted inside.
6. Optional: Warm your favorite marinara sauce in a saucepan over low heat and serve alongside the meatballs for dipping or drizzling.

One thing I’ve learned from decades in the kitchen is that you need to trust your instincts. If the meatballs aren’t browning evenly, adjust the heat a little. Cooking should be a joy, not a chore.