In the port it's self, Cantina Latina offers typical Americanized Mexican. There is a taco kiosk that does serve good street tacos. At one time El Faro, a seafood restaurant was at the port, not sure if its still there.
Most of the beach clubs along the malecon in Mahahual serve what isn't "authentic" Yucatan or Quintana Roo food but reasonably familiar dishes to American tastes; the seafood dishes are pretty decent.
La Chilangaloense, along the malecon, probably has the most diversified menu, with aquachile fish, molcajeteado, some interesting seafood tacos and a couple of variations of ceviche. Also cajeta is available. The food att eh AI beach clubs tends to be a bit better than the pay-go beach clubs.