How to select true/false based on column value?

Use a CASE. I would post the specific code, but need more information than is supplied in the post – such as the data type of EntityProfile and what is usually stored in it. Something like:

CASE WHEN EntityProfile IS NULL THEN 'False' ELSE 'True' END

Edit – the entire SELECT statement, as per the info in the comments:

SELECT EntityID, EntityName, 
       CASE WHEN EntityProfile IS NULL THEN 'False' ELSE 'True' END AS HasProfile
FROM Entity

No LEFT JOIN necessary in this case…