The good fat burger

Ingredients

• 1 brown onion, finely chopped
• 1 long fresh green chilli, deseeded, finely chopped
• 2 tbs finely chopped fresh coriander
• 2 tbs finely chopped fresh flat-leaf parsley
• 2 tbs finely chopped preserved lemon
• 2 tbs lemon juice
• 2 garlic cloves, crushed
• 1 tsp ground paprika
• 1 tsp ground cumin
• 1 tsp ground coriander
• 1 tsp ground turmeric
• ½ cup (125ml) olive oil
• 600g chicken thigh fillets, fat trimmed
• 1 orange sweet potato
• 3 cups (750ml) vegetable oil (for frying)
• 2 limes, juiced
• 100ml sour cream
• 2 tbs finely chopped red onion
• 4 seed burger buns, split
• 8 oakleaf lettuce leaves
• 2 avocados, sliced