You will find great threads in the feeding section of which veg can be given. The list is very long so it’s probably best to check it out! They can eat a wide variety of veg and rotating them is great to do. Some things shouldn’t be given too often though due to high calcium levels such as parsley, kale, spinach. Brassicas (broccoli, cabbage etc) can cause bloating. Tomatoes are acidic.
Cucumber is fine to give daily. mine generally get a base of lettuce (not iceberg), bell peppers (excellent for vit c), coriander, cucumber and then I’ll add in a bit of something else in rotation (and some things don’t get given very often as mentioned above) - spring greens, herbs, baby sweetcorn, a bit of tomato, chard, spinach, rocket, green beans
I don’t give fruit very often.
As I say though, look through the feeding lists, they are very helpful in what can be given and whether they are suitable for regular feeding or whether they should be used more sparingly.