In a large saucepan, Add butter and flour and cook over medium high heat, stirring occasionally until tender now add salt and oregano. Cook and stir one minute. Add milk,.Cook and whisk until thickened and bubbly all over.Stir in shredded cheddar until melted. Add hot, drained vegetables to saucepan, stirringto coat evenly with the sauce.Pour vegetables and sauce into deep one quart casserole dish.