"Most come out huge" - because they are overgrown (the ones, which are almost white on your photos are very old by standards of Russian villagers or dacha-owners). The ones which are on the first photo still on the plant - they are ready to be picked up. If they stay one or 2 days longer on the plant - they start losing water, become harder, seeds become bigger and you lose the central part of the cucumber, because seeds part starts to taste worse . If more than 2 days - it would be time to throw them away or at best use for pickling (salt destroys nuances of taste).

I make salad like yours too! In Russia people make it without avocado. But avocado makes it even better!