Heat the oven to 190°C (Gas Mark 5 / 375°F).Spread the flour on a plate. Lightly beat the egg with the milk in a bowl. Spread the breadcrumbs in a third dish.Cut the avocado into fairly large dice. A few chunks at a time, roll in the flour until all sides are coated. Shake off any excess, then dunk into the egg mixture, again ensuring that it is well coated. Finally, roll in the breadcrumbs. For a thicker coating, repeat the egg and breadcrumb steps for a second time. Lay the finished pieces out on a lightly greased baking sheet, ready to be cooked, and then do the same process with the next few chunks of avocado.When all the avocado has been breaded, bake for around 20 minutes, or until the breadcrumbs are crispy and golden (cooking time may vary depending on the type of breadcrumbs you used, so check them occasionally).While the poppers are baking, prepare the coriander-lime mayonnaise. Place the coriander and lime juice in a mini food processor, and blitz well. Then add the mayonnaise and seasoning to taste, and continue to blend until you have a fairly smooth mayonnaise.Serve the warm avocado poppers with the mayonnaise.