Blanch the green beans and asparagus in boiling water for 2-3 minutes and then rinse with cold water and drain.
Cut the cucumber in half lengthwise, scrape the seeds out, then slice into crescent-shaped pieces.
Cut the tomatoes into wedges.
Slice the radishes.
In a serving bowl, mix the vegetables and watercress. Add the mint leaves.
Cut the halloumi into 1 cm thick slices, brush with oil, then grill, barbecue or griddle them until slightly charred.
Put the cheese slices on top of the salad.
Mix the oil with the lemon juice and the sumac and drizzle over the salad.