1 pound jumbo lump crab, drained and picked
1 sweet onion, finely chopped
1/2 cup vegetable oil
1/2 cup cider vinegar
1/2 teaspoon salt
1/2 teaspoon black pepper
2 tablespoons fresh flat-leaf parsley leaves
Combine first 7 ingredients in a large bowl, stirring gently. Cover and chill at least 2 hours. Top avocado slices with crab mixture using a slotted spoon.