Pulled pork sloppy joe dogs

Name: Pulled pork sloppy joe dogs
Ingredients: 1 tbsp sunflower oil; 2 onions, halved and sliced; 1 tbsp garlic powder; 3 garlic cloves, sliced; 1 tbsp tomato purée; 1 tsp dried oregano; ½ tsp smoked paprika; 500ml chicken stock; 400g pulled pork (shop-bought, or get a recipe here on bbcgoodfood.com); 2 green peppers, chopped into small pieces; 1 green chilli, sliced; 1 tbsp American mustard, plus extra to serve; 8 hot dogs; 8 hot dog buns; soured cream, shallots finely sliced into rings and toasted yellow mustard seeds, to serve