In a skillet over medium heat, warm a splash of olive oil, then add finely chopped spinach and minced garlic. Sauté for 3-4 minutes until cooked. Remove from heat and cool.

In a large mixing bowl, combine ground beef or turkey with cooled spinach and garlic mixture, egg, breadcrumbs, Parmesan cheese, Italian seasoning, salt, and pepper. Mix gently.

Scoop a portion of the mixture, flatten it, place mozzarella cube in the center, wrap meat around it, and roll into a ball.

Preheat oven to 400°F (200°C) or heat skillet for pan-searing. Bake for 20-25 minutes until golden or pan-sear for 6-8 minutes per side until internal temperature reaches 160°F (70°C).

(Optional) Simmer cooked meatballs in marinara sauce for 5-10 minutes for added flavor.

Let meatballs rest for 5 minutes before serving.