Hot dog wraps with fiery onion relish recipe

Ingredients

• 6 giant hot dogs (loose or canned)
• 6 Lebanese flatbreads or flour tortillas
• Squirty yellow mustard (optional)
• Watercress, to serve
• 2 tbsp sunflower oil
• 3 red onions, thinly sliced
• 1 garlic clove, thinly sliced
• 1 tsp yellow mustard seeds
• 1 tsp cumin seeds
• 3 tbsp light muscovado sugar
• 4 tbsp red wine vinegar
• Large pinch crushed chilli flakes