1. To make the dressing, purèe the mango, oil, lime zest, and juice in a food processor or blender. Season with salt and pepper, adding a little water if too thick.

2. Toss the shallot, cilantro, and mint with the salad greens in a large bowl. Add a few spoonfuls of dressing and toss again. Divide among 4 plates and top each with equal amounts of crab and avocado. Serve at once, passing the rest of the dressing on the side.