Combine the tomato, avocado, coriander, onion, lime juice, Tabasco sauce and a pinch of salt in a medium bowl. Cover and refrigerate while you prepare the crab cakes.
Combine the bread and milk in a medium bowl. Add the crab and mayonnaise, stirring to combine. Shape into 8 cakes and dredge in the breadcrumbs.
Preheat the oven to 200°C. Heat the oil in a large nonstick frying pan over moderate heat. Fry the crab cakes for 2 minutes on each side or until golden brown. Transfer to a baking tray and bake for 5 minutes or until heated through. Serve the cakes with the relish.