The basic (flat) route is
https://sf2g.com/bayway.html but given the construction in the last 10+ years we should probably update that strava track. I haven't ridden it in years so I can't really help with it. I used to work in Foster City though and used Hillsdale caltrain!
Depending on how comfortable you are with merging with cars, there's a few different ways to do the last leg:
* Hillsdale Blvd -> Saratoga -> Frankllin Blvd is a straight shot but has merges going across 101, probably the most traffic (blue line)
* E 3rd ave -> S Delaware: probably the one I'd recommend, E 3rd has a bike path in the center of the overpass (accessible by crosswalks w/ signals) and S Delaware has (unprotected) bike lanes but is otherwise a straight shot. (purple line)
* There's also this little path thingy from Fashion Island blvd that ends up on 19th Ave -> S Delaware, but I don't think I've ever taken that route across the water. 19th ave iirc was fine but fairly industrial. (yellow)
the red line is the route from the link
