Preheat the oven to 400 degrees, cut the squash half in half, removed seeds and put on a lined baking sheet, drizzle with olive oil, salt & pepper and roast for about 30 – 45 minutes depending on your squash. It needs to be tender. Leave the squash until cool enough to handle and scoop out the soft flesh into a large bowl.
Meanwhile heat some oil in a frying pan over a medium heat and add in the onions, celery, cilantro stalks, lemongrass and chilli with a pinch of salt and cook for about 5 minutes until the onion is translucent. Then add in the garlic and ginger and cook for another 2 minute. Mix this into the squash with the chopped cilantro leaves and mix everything together well. Add in the cornflour and panko. Season with salt & pepper and taste.
When they have come to room temperature place one wonton wrapper on a board or work surface so it is a diamond shape. With your finger moisten the edges of the wrapper with the beaten egg. Take a small teaspoon of the filling and put it in the top triangle of the diamond away from the edges.
Fold the bottom half over the filling and seal the edges with your fingers. Push down around the filling to get rid of any air. Make sure the edges are sealed and there is no filling escaping. Moisten the two bottom corners with egg and close them together and seal to create the dumpling shape.
Continue until you have made enough wontons.