Heat 2 tablespoons of the oil in a nonstick pan and fry the onion for about 4 minutes, or until the onions are soft. Add the ginger and garlic, and cook for another 40 seconds. Stir in the coriander, red chile powder, garam masala, and salt, to taste, and cook for another 20 seconds then take the pan off the heat. Place the mixture into a large bowl.
Add the lemon juice, fresh cilantro, crab, egg, and mayonnaise to the onion mixture in the bowl. Stir the ingredients well and add the bread crumbs. Divide the mixture into 8 equal portions and form each into a circular shape.
Heat 1 tablespoon of oil in a nonstick pan and cook the crab cakes in batches over a low, moderate heat for about 2 minutes on each side, or until the crab cakes are golden brown, adding more oil as needed.
Place the cooked crab cakes on a baking sheet and place them into the oven to stay warm while you cook the others.
For the tamarind mayonnaise: Place the mayonnaise, milk, tamarind paste, black pepper, salt, to taste, and cilantro into a bowl and whisk together. Adjust the seasonings, to taste.
To serve the crab cakes, take the warm crab cakes out of the oven, and put them on a plate and serve with a spoonful of the tamarind mayonnaise. Place the fresh lightly dressed salad leaves on the side.