It's been about 10 years since I've been there but the best place to eat in Lethbridge was Miro Bistro and it wasn't even close when I was there. Good food, cozy vibe and you'll probably meet Miro if it's still open which it seems to be - he liked to come out and chat with the guests, his pride in his cooking is off the charts and he was a great guy. It was one of the only unique places in Lethbridge for a nice dinner out.
https://mirobistro.ca/
There was a place in the water tower that was kind of novel, going for the earls/keg/moxies vibe. Food was just OK... more of a novelty kind of place at the time.
Also a restaurant in the fire hall downtown that was better than the water tower but not as good as Miro's but I can't find any mention of it online, maybe it closed.