Sauté 2 cups of fresh spinach and 2 minced garlic cloves in a skillet over medium heat with olive oil for 3–4 minutes until wilted.

In a large mixing bowl, combine 1 pound of ground beef or turkey, 1 beaten egg, ½ cup of breadcrumbs, ¼ cup of grated Parmesan cheese, and the sautéed spinach and garlic. Add 1 tablespoon of Italian seasoning, salt, and pepper. Mix gently.

Scoop a portion of the mixture, flatten it, place a mozzarella cube in the center, and form into a ball. Repeat until all mixture is shaped into meatballs.

Preheat the oven to 400°F (200°C) and place the meatballs on a parchment-lined baking sheet. Bake for 20–25 minutes until golden brown and the internal temperature is 160°F (70°C).

Transfer the baked meatballs into simmering marinara sauce for an additional 5–10 minutes for extra flavor.

Let the meatballs rest for 5 minutes on a serving plate before serving.