Preheat the oven to 375°F.
In a skillet, heat olive oil over medium heat. Add the chopped onion and cook until translucent, about 3-4 minutes. Add the minced garlic and cook for an additional minute until fragrant.
In a large bowl, combine the mashed potatoes, chopped spinach, cheddar cheese, sour cream, milk, salt, pepper, and paprika. Mix well until all ingredients are fully incorporated.
Spread the potato and spinach mixture evenly into the pre-made pie crust.
Bake in the preheated oven for 30-35 minutes, or until the pie is heated through and the top is slightly golden.
Let the pie cool for 5-10 minutes before slicing and serving.