Preheat your oven to 375°F (190°C).
Heat olive oil and butter in a large skillet over medium heat.
Add onion and garlic and sauté until translucent, about 3-4 minutes.
Stir in the shrimp and crab meat, and season with Cajun seasoning. Cook for 2 minutes.
Add the chopped spinach and cook until wilted.
Reduce heat to low and mix in cream cheese until melted and smooth.
Stir in mozzarella, sour cream, and mayonnaise. Season with salt and pepper.
Transfer the mixture to an oven-safe baking dish and bake for 15–20 minutes until bubbly and lightly golden on top.
Garnish with chopped green onions or parsley and serve warm with crackers, baguette slices, or chips.