1. Sprinkle salt over the onions and let stand for about 5 min. Then rinse the onions and press out as much liquid as possible.
2. Toast the bread and cut it into cubes for the croutons.
3. Break the feta up into small pieces.
4. Toss the spinach with the oil and arrange on a platter with the cucumber, beans, onions and feta.
5. Sprinkle with mint, lemon zest, pepper and some of the croutons.
6. Serve the salad with grilled chicken or salmon and the rest of the croutons.