Ultimate veggie burger with pickled carrot slaw

Name: Ultimate veggie burger with pickled carrot slaw
Ingredients: 2 tsp vegetable oil plus extra for frying; 1 small onion diced; 2 garlic cloves chopped; 2 large Portobello mushrooms finely chopped; 2 small sweet potatoes peeled and diced; 150g cooked quinoa; 1 large beetroot grated; 1 egg beaten; 2 tbsp chopped coriander; zest 2 limes; 4 tbsp plain flour plus extra for dusting; 1 large carrot thinly shredded; 2 tbsp rice wine vinegar; 1 tsp golden caster sugar; 2 tbsp mayonnaise; 1 tbsp chilli sauce; 4 burger buns lightly toasted; 2 handfuls rocket or spinach leaves