Preheat your oven to 375°F (190°C). Lightly grease a baking dish or oven-safe skillet.
In a skillet, heat the olive oil or butter over medium heat. Add garlic and cook for 30 seconds, then add spinach. Cook until wilted and moisture has evaporated. Remove from heat.
In a large mixing bowl, combine softened cream cheese, sour cream, mayonnaise, and seasonings. Stir until smooth and creamy.
Add cooked shrimp, crab meat, sautéed spinach, mozzarella, and Parmesan. Mix until evenly combined.
Transfer the mixture into the prepared baking dish. Sprinkle additional mozzarella on top. Bake for 20–25 minutes, until bubbly and golden on top.
Let the dip cool slightly before serving. Pair with crostini, tortilla chips, crackers, or sliced vegetables.