As an incoming freshman studying chemical engineering at UCD, what would be some interesting (not necessarily easy) general education classes to take? I’m interested in astronomy, food science, and energy. I have room in my first quarter for two GEs, so any suggestions would be nice! 
NUT10 with Professor Applegate but super tough to get a spot until Junior/Senior year.
Do you mean GE as in fulfilling GE requirements, or GE as in “any filler class”? Because in the first case, you’ll need to take classes that fulfill arts/humanities and/or social science requirements. ChemE major requirements already fulfill all science/engineering requirements, so taking something like nutrition would be useless if you’re looking at classes that fulfill GE requirements. It’d be a good choice for a filler class that’s not meant to fulfill any requirements though.
On that note, a few arts/humanities and/or social science GEs I’d personally recommend: LIN 1 (intro to linguistics), ANT 2 (cultural anthropology), any of the RST 1 series (compares religions on various issues depending on the exact class)
If you’re looking for a writing experience GE and aren’t concerned with the AH/SS requirements, ANS 42 (companion animal biology) is usually offered in winter.
If you’re interested in astronomy, look into AST 10G or 10S if you want filler units. I took AST 10S one summer for filler units, and it was both interesting and one of the easiest As I’ve ever taken.
If you like history, my son and his best friend (civil engineer) took Classics CLA10 and CLA03. These fulfill the Humanities GE requirements, also have to give ANT2 a thumbs up.