On a mandoline slice 1/2 Cabbage, 1 Fennel Bulb, 1/2 Sweet Onion [I used shallot which isn’t sweet but oh well] and 1/2 Cucumber [already sliced lengthways].
Toss sliced veggies in a bowl with a couple tablespoons of olive oil and lemon juice from 1/2 lemon. A 2:1 ratio of fat to acid. Season with salt and pepper. Let marinade in the fridge until you serve.