Fortigate 100e routing thru a Cisco ASA (on same network)

Hi everyone.

New to the forum and (partially) new to Fortigate firewalls.

We have a Fortigate 100e (6.0.4) with a hardware switch running 6 vlans, one being 10.21.50.1. This is going to replace (at some point) a Cisco ASA. However, for the time being the ASA is protecting another (gov) network and must remain in place. The interface of the ASA for the gov network is 10.100.201.1. Both firewalls have routes to the internet and that part is working ok. 

We need clients in the 10.21.50.1 network to reach resources in the 10.100.201.1 network and can’t figure out the static route or how-to setup the link. I know it’s something simple, but it’s escaping me. I was thinking of direct connecting the ASA to the Fortigate, each with a separate available port, and then setup a static route and the policies. Is there a simpler way?

Thank you