Unfortunately, OPENQUERY doesn't support dynamic parameters.
However, you could change your query to use EXEC...AT:
EXEC('
SELECT *
FROM MyTable
WHERE Field1 = ?' , 'A'
') AT ALinkedServer
You may get error "Server 'ALinkedServer' is not configured for RPC."
In that case you need to enable RPC:
exec sp_serveroption @server='ALinkedServer' , @optname='rpc', @optvalue='true'
exec sp_serveroption @server='ALinkedServer' , @optname='rpc out', @optvalue='true'