Unusual as this salad sounds, it really works because of the pairing of salty feta with sweet watermelon. In Greece, where it originates, they’ll often throw in some black olives too but I like the crunch you get from the toasted pecans. Don’t make this salad ahead or the salty cheese and nuts will draw the moisture out of the watermelon, making them all soggy.
Break up the pecans and lightly toast in a dry frying pan with a pinch of salt until golden. Remove and lightly crush in a pestle and mortar. Leave to cool.
Place the watermelon in a serving bowl and mix in the cucumber. Crumble in the feta and mix well, seasoning with a little salt and pepper and a drizzle of olive oil. Add the mint leaves, pecans, sumac and lemon juice to taste. Toss lightly and serve.