Very interesting ... It doesn't really look like scale. What it looks like are leaf galls. Some insect larvae get in the leaf and induce it to produce the swelling which they live in until they are ready to become adult and leave. Aphids can do this and midges and others. HOWEVER, I have only ever seen this on woody plants-- my hackberry trees get covered in them every year and the witchhazel shrub had them last year (different species of insects--each tree has it's own specialized gall insect, the Hackberry gall psyllid lives only on hackberrys) On the trees, they are not really an issue, the galls don't damage the trees. But I have never seen them on veggies like this and it looks like a serious infestation.
Diagnostic test would be can you rub them off? Scale insects can be rubbed off; the galls would be part of the structure of the leaf.
If they are scale insects you can use a brush to touch each one with rubbing alcohol, which will kill them. If they are galls the insect is well protected inside the leaf and pretty immune to any kind of treatment except removing the leaf and destroying it.