Heat the olive oil in a pan, add the red onion, and cook for 1 minute. Add the curry powder, cook for 2 minutes, allow to go cold.
Cut the avocados in half, remove the skins and stones.
Place the avocados in a blender, add the remaining ingredients except the sour cream plus the spiced onion mix. Whiz into a coarse purée, then fold in the sour cream.