The piece in your picture is on the driver side, correct? If so it looks like it is p/n 77277-35040, fuel pipe shield.
#13 at this link.
Fuel System Components for 2014 Toyota 4Runner | Discount Toy
There is no similar piece on the passenger side, only on the driver side to shield the fuel pipe. The only thing on the passenger side is the mud flap so you aren't actually missing anything.