SQL Server Scalar variable in Inline table valued function

I have a multi statement table valued function which I would like to change to an inline table valued function for optimization purposes ( I don't really know if that will be an optimization but I want to try that anyway ). My problem is that I have a scalar variable which I don't know how to put in my WITH statement.

Code example:

CREATE FUNCTION [dbo].[function]()
RETURNS 
  @return_table table (id INT,value NVARCHAR(500)) 
    AS
    BEGIN
      DECLARE @tmp_table        TABLE(id INT, value VARCHAR(500))
      DECLARE @variable     BIGINT
      INSERT INTO @tmp_table [...insert code...]
      SET @variable = (SELECT MAX(id) FROM @tmp_table)
    INSERT INTO @return_table SELECT id,value FROM @tmp_table WHERE id = @variable
RETURN

This code is an example, the actual function is more complex but the problem is exactly the same

I could easily change this to a single WITH statement like this:

CREATE FUNCTION  [dbo].[function]()
RETURNS TABLE
AS
RETURN 
(
    WITH tmp_table AS (
       SELECT [...Select Code...]
    )
    SELECT id,value FROM tmp_table 
    WHERE id = [variable]
);
GO

My problem lies into the [variable] which I don't know how to put into the query. Also, the variable is used more than once in my function so I'd rather not just replace it with the query.

I also tried this approach:

CREATE FUNCTION  [dbo].[function]()
RETURNS TABLE
AS
RETURN 
(
    WITH tmp_table AS (
       SELECT [...Select Code...]
    ), variable = (SELECT MAX(id) value FROM tmp_table)
    SELECT id,value FROM tmp_table 
    WHERE id = (SELECT TOP 1 value FROM variable)
);
GO

But is seems like it made the function way slower.

Thank you.