Personally, I think a food festival is a bit ambitious seeing as we seem to have trouble opening the Grab-N-Go places we already have, but I digress.
If USH hosted a food festival, I think the best way to organize it would be to have a central hub in the Universal Plaza, with five or six booths set up around the outside and seating in the middle. In addition to that, there would be a few small booths set up in the various areas around the park, themed to fit into their surroundings (e.g., Fish & Chips in Baker St., Egyptian Themed by RotM). This is using the Epcot Food & Wine festival as a template, I'm not sure how they did it at California Adventure.
For a theme, I think the best way to go would be bringing it back to either classic (Universal) films and film franchises or do a sort of "Old Hollywood" theme. In the last decade, the park has become less focused on Universal IP, with fewer and fewer attractions based on NBCUniversal properties. With Super Nintendo World coming down the pipe, so to speak, that trend will only continue. In my opinion, since one of the very few remaining things that separated USH from "Unique Park-Going Experience" and "UO, but with less stuff" is the active movie and television studio and accompanying Studio Tour, I'd like to see them acknowledge that aspect a bit more.