Combine all ingredients in a blender or food processor until fully pulverized. The mixture should be crumbly but stick together if you press on it. If it doesn't stick, add a bit more nondairy milk until it does.
Press the filling into two 5-inch tart pans and set in the freezer to cool.
For the avocado key lime tarts:
Combine all ingredients in a blender or food processor until completely smooth. Taste for sweetness and adjust if needed.
Spread the mixture onto the prepared coconut graham cracker crusts, and return to the freezer for at least 2 hours.
Slice and enjoy. Store leftovers in the freezer.
Notes
Be careful not to zest the white parts of the limes - they will make the mixture taste too bitter.For a gluten-free option, use gluten-free graham crackers. For a raw option, use a nut-based crust.