Cook pasta in salted water and drain.
Melt the butter in a medium saucepan then remove from heat. Whisk in the flour, salt, pepper, oregano and garlic to create a roux.
When the roux is smooth and bubbly, slowly stir in the milk. Return to heat and bring to a boil, stirring regularly. Reduce heat and simmer for one minute.
Remove the saucepan from heat and add the cooked macaroni and manchego cheese, stirring until the cheese is melted. Serve hot.