Combine all the ingredients for the crust, except the water in a food processor and process until they come together. Add water with processor running until mixture holds together when pinched. You may not need the water if your dates are fresh enough. If they're too dry, the water might be necessary. Add slowly, you won't need much at all.
Press mixture into the base and all the way up the sides of 3 mini (4 inch) tart shells.
Place the crust shells in the freezer to set while you make the filling.
For the filling
Combine the avocado, lime juice, lime zest and agave in the food processor and process until smooth and creamy, scraping down sides as needed.
Remove crust shells from the freezer and pour the filling evenly into each shell. Smooth the tops with a spatula, place tarts on a baking sheet and return to freezer for at least 1 hour to set up to overnight. If tarts are difficult to remove from the shell upon serving, place the bottoms in a hot water bath for 10 seconds and they'll pop right out.
Store in the freezer in an airtight container or bag to prevent freezer burn.