Island Ahi burgers with coriander-chilli-lime sauce

Ingredients

• For the sauce
• 2 chilli peppers
• 120ml mayonnaise
• 3 tbsp sour cream
• 3 tbsp finely chopped coriander leaves
• 1 tbsp fresh lime juice
• 2 tsp minced fresh ginger
• 1 tsp minced garlic
• 1/4 tsp salt
• For the burgers
• 1 egg
• 45g panko (Japanese breadcrumbs)
• 4 tsp soy sauce
• 4 tsp sugar
• 1 tbsp sesame oil
• 1 tbsp minced fresh ginger
• 1 tbsp minced garlic
• 2 tsp fresh lime juice
• 1 tsp grated lime zest
• 1/2 tsp crushed chilli flakes
• 1/2 tsp salt
• 700g tuna fillets, finely chopped
• 1 tbsp vegetable oil
• For the assembly
• 4 seeded Kaiser rolls, split
• 1 large Maui onion (or other sweet onion), thinly sliced
• 1 large vine-ripened tomato, sliced
• 1 package radish or sunflower sprouts