Put the yogurt in a bowl and stir in the cornstarch. Add mayonnaise and whisk in the vegetables and seasonings. Go very easy on the salt and pepper.
Cover bowl and put aside for 15 minutes or so for the flavors to marry. Correct seasoning. Gently fold in the crabmeat. Reserve, refrigerated, if you are doing this in advance.
Preheat oven to 425 degrees. Arrange natural or ceramic shells or ramekins on a baking sheet. Divide crab mixture among containers, mounding it a bit in the center so that it looks generous.
Sprinkle the breadcrumbs over the crab mixtures. Bbake on the top rack of the oven until bubbly and lightly browned, 10 – 15 minutes.
Serve hot.