Cut spinach into bite-sized pieces and mince the garlic.

Rinse oysters gently under water and pat dry with paper towels. Season with salt and pepper.

Boil water in a pot and cook spaghetti 1 minute less than the package instructions. Drain well.

Heat olive oil, butter, and garlic in a pan over low heat until fragrant. Add oysters and cook on medium heat until they change color. Add spinach and sauté for 1 minute until wilted.

Add flour to the pan and stir until no longer powdery. Pour in milk, salt, and pepper, and bring to a gentle boil. Add spaghetti and toss to coat evenly.