Combining expressions inside each other

I am trying to make the expression build the email for new employees. Its real simple, first inital, last name. I cannot seem to combine a concat and a charat in the same expression so it can scrape the first inital of the first name, get the last name from the ticket, and then combine it all together. 
I was thinking

concat(

'charAt('{{ticket.onboarding_request.actor_1.cf_employee_name}}', 0)',

 '{{ticket.onboarding_request.actor_1.cf_employee_last_name}}')

Result: charAt('Value 1', 0)Value 2

But this does not work. I have tried to play with the parenthesis and quotes, so if one is off here that isnt the problem