Quick chicken souvlaki

Name: Quick chicken souvlaki
Ingredients: 1 small red onion, finely sliced; 25g green pitted olives, chopped; ½ cucumber, halved lengthways and thinly sliced; 140g cherry tomatoes, halved; small bunch parsley or mint (or a mixture), leaves picked; 1 cooked beetroot, coarsely grated; 2 ready-roasted chicken breasts, torn into small pieces; 100g natural yogurt; 3 flatbreads or pitta breads; drizzle of extra virgin olive oil