Is there a solution for "SELECT OR INSERT"

given a simply table table like this:

create table MyTabl 
(id serial,lname varchar,primary key (id)
)

I am trying to return the Primary-Key for a given
row regardless of the wanted row already being 
in the table.

using something like:

select coalesce 
( (select id from MyTabl where lname='wanted'), (insert into MyTabl (lname) values ('wanted') returning id)
) as id;

the above doesn't allow the insert..returning even thow
a similar select statement would be okay.
Is there a way to get the ID row OR create a new one in
ONE single statement?

my best regards and thank-you 
for your time....

Stefan