Preheat the oven to 170C/325F/Gas 3.
Heat half the oil in a non-stick pan and fry the onion for about four minutes, or until soft. Add the ginger and garlic and cook for another 40 seconds. Stir in the coriander, red chilli powder, salt and garam masala and cook for another 20 seconds then take off the heat. Place into a large bowl.
Add the lemon juice, fresh coriander, crab, egg and mayonnaise to the onion mixture in the bowl. Stir well and add the breadcrumbs. Divide into eight equal portions and form each into a circular shape.
Heat one tbsp of oil in a non-stick pan and cook the crabcakes in batches over a low moderate heat for about two minutes on each side, or until golden brown adding more oil as needed.
Place the cooked crabcakes on a baking tray and place them into the oven to stay warm while you cook the others.
For the tamarind mayonnaise, place all the tamarind mayonnaise ingredients into a bowl and whisk together. Season to taste.
To serve, take the warm crabcakes out of the oven, put them on a plate and serve with a spoonful of the tamarind mayonnaise. Place the fresh lightly dressed salad leaves on the side.