Wash, dry, and cut the avocado in half lengthwise. Sprinkle the half with the pit with lemon/lime juice, wrap tightly in plastic wrap, and place in the fridge (use within a few days for another meal). Scoop out the flesh from the other half with a spoon and cut it into smaller pieces.
Place the avocado in a blender container. Add coconut milk, flour, sweetener, baking powder, a few drops of vanilla flavoring, and a bit of water (a few tablespoons). Blend into a thick, smooth batter.
Transfer to a small ovenproof dish, ramekin, or muffin mold (fill up to ¾ of the height). Smooth the top.MICROWAVE: Place the dish with the batter in the microwave for about 2-3 minutes (depending on the microwave's power). Check occasionally and test for doneness. Remove the muffin when it rises and is dry on top.OVEN: Place the dish with the batter in a preheated oven at 180°C (350°F) for about 20-30 minutes. Remove the muffin when it rises and is golden brown.
Enjoy warm or cold.