Feta and greens filo triangles

Name: Feta and greens filo triangles
Ingredients: olive oil spray; 1 onion, finely chopped; 4 garlic cloves, finely chopped; 250g/9oz cavolo nero, trimmed of thick stems and roughly chopped; 250g/9oz spinach, roughly chopped; 250g/9oz chard, chopped (including stems); 250g/9oz reduced-fat feta cheese, crumbled; 50g/1¾oz pine nuts, toasted; bunch of dill (20g/¾oz), roughly chopped; ½ nutmeg, freshly grated; 1 unwaxed lemon, finely grated zest only; 6 sheets of filo pastry, each 45cm x 25cm/17½ in x 9½ in; salt and freshly ground black pepper; sesame seeds, for sprinkling; 50g/1¾oz caster sugar; 50ml/2fl oz red wine vinegar; 400g tin chopped tomatoes; ½ tsp dried chilli flakes