Gyros

I use it as a "sauce" for steamed veggies, especially broccoli.

Use it as a marinade on baked chicken.

These are good

https://www.budgetbytes.com/beef-kofta-meatballs-with-roasted-vegetables/

Or with spinach pie

https://www.budgetbytes.com/spinach-pie/

Potato salad?

Good dip with vegetables
I put it on pita sandwiches with meat

I like it with a spoon

if you like pizza with ranch sauce, you will love pizza (hot or cold) in tzatzki sauce

I was in this position a month or so ago and someone on here suggested marinating chicken breasts in the tzaziki and then grilling - I did it although made in oven due to weather and it great - subtle tzaziki taste but very moist and overall flavorful.

You could use it just for dipping with pita. Or make meatballs and have with that. Off the top of my head, I'd do lamb or beef meatballs with it.

Any ideas for leftover tziziki sauce? I have been eating it on falafel salads and bowls but am sick of that.