Mix the mayonnaise, yoghurt, honey, 15 ml (1 tbsp) of the curry powder and half the lime zest and juice together. Season with salt and pepper.
Heat a good splash of oil in a frying pan on a medium-high and fry the onion for about 10 minutes until caramelised. Stir through the remaining 15 ml (1 tbsp) curry powder, garlic and chilli, if using and cook for 1 minute.
Add the shrimp to the onion mixture and cook for 1 minute or until pink. Stir through the remaining lime zest and juice. Season with salt and pepper.
Stone, peel and cut the avocado into 4 wedges. Place a wedge and lettuce leaf in each of four serving glasses. Add the shrimp mixture and dollops of the sauce.