Preheat oven to 350 degrees F and have ready a 8 inch round deep sided baking dish. An equivalent size will do.
In a large saucepan set over medium heat the olive oil and about half of the garlic. Stir for a minute and add the leeks. Cook, stirring occasionally for about 5-8 minutes. Remove leeks from pan and reserve pan.
Cook pasta according to package, drain and set aside.
In the reserved saucepan set over medium to high heat, melt butter with remaining garlic until sizzling. Whisk in flour until you have a paste. Gradually start whisking in your milk. Continue doing this until you have added all the milk and you have a slightly thickened sauce. Reduce heat to medium low and add most of the cheese, reserving a little for the top. Stir really well until all the cheese has melted into the sauce. Season with a little bit of salt and pepper and add the oregano. Stir and remove from heat.
In a bowl combine the bread crumbs, remaining cheese and fresh parsley. Stir to combine.
Pour the pasta, leeks and sauce into your prepared dish. Stir and cover with the bread crumb topping. Bake for 25-30 minutes. Remove from oven and leave few minutes before serving.
*A note on times provided: appliances vary, any prep and/or cook times provided are estimates only.