create function foo (@a int)
    returns int
as
begin
    return @a
end

-- clear out the plan cache
dbcc freeproccache
dbcc dropcleanbuffers
go

-- use the function
select dbo.foo(5)
go

-- inspect the plan cache
select * from sys.dm_exec_cached_plans
go

select * from sys.dm_exec_query_plan(<insertplanhandlehere>)

CREATE FUNC dbo.Foo ()
RETURNS TABLE
AS
RETURN (SELECT ...)
GO