Make the Coulis: In a small saucepan, combine the raspberries, stevia, and 1/2 cup water and bring to a boil. Reduce the heat to low and cook for about 10 minutes. Remove from the heat and push the mixture through a fine-mesh strainer into a clean bowl. Whisk in the lemon juice. Let cool to room temperature.
Make the Mousse: Halve and pit the avocado. Scoop the avocado flesh out of the skin using a spoon and drop it into a food processor. Pulse the avocado until smooth.
Add the cocoa powder, almond milk, stevia, and 1/2 cup water and pulse again until completely blended and smooth.
Evenly distribute the mousse among four martini glasses, champagne flutes, ramekins, or mason jars and divide the raspberry coulis among them. Chill for at least 1 hour before serving.
Before serving, top as desired and eat it up with a spoon!