Add all key lime mousse ingredients to the blender and blend until completely smooth. Set aside in refrigerator to chill and thicken

Add aquafaba and cream of tartar to a stand mixer bowl (or use a hand-held mixer) and whip on high speed until liquid becomes light and fluffy. This might take about 5 minutes.

Slowly add powdered sugar and continue whipping until stiff peaks form, maybe 2-4 more minutes. Taste and adjust sugar as needed.

To assemble parfaits, use clear glasses so you can see the pretty layers! Add some optional crushed graham crackers, followed by a layer of mousse, then a layer of aquafaba whipped cream. Keep adding layers to fill the cup and top with a thin slice of lime or lime zest.