passing attributes

A few typo's that may or may not be in your actual code:

<cfoutput>#firstname</cfoutput>

Should be

<cfoutput>#firstname#</cfoutput>

or better yet

<cfoutput>#arguments.firstname#</cfoutput>

and

<cfinvoke component="toastcfc/header" method="header"  firstname="john" lastName="kidd">

Should be

<cfinvoke component="toastcfc.header" method="header"  firstname="john" lastName="kidd" />

Let's assume that your actual code is correct. In that case you must have a directory called toastcfc (or a mapping) and in it a file called header.cfc and in it a function called header. What does the actual code in the <cffunction ... > look like? Do you have a <cfargument name="header" type="string"> tag?