Preheat the oven to 190°C/fan 170°C/gas mark 5. Process the cashew nuts and the xanthan gum in a liquidiser until it forms a fine powder.
Add the dates and 1 tbsp water and continue to process until a smooth paste is formed.
Lightly grease a 4-hole muffin tin. With wet hands, divide the mixture into 4 balls and place one in each hole. With your finger wrapped in cling film, press the mixture into the base and up the sides. Bake in the oven for 5-6 minutes until firm. Leave in the tin to set, then carefully move on to a cooling rack.
Place the stem ginger, avocado and lime zest into a bowl and whizz with an electric mixer until smooth. Add lime juice to loosen the mixture, but keep it firm. Pipe the mixture into each tartlet. Keep refrigerated until required.