Blend 3 cups pecans and dates in a food processor until finely ground, about 1 minute. Pour agave nectar over nut mixture and process until fully incorporated, about 30 seconds. Press nut mixture evenly into prepared pie pan.
Peel and pit persimmons, then puree in food processor until smooth. Pour over crust and smooth out. Garnish with chopped pecans and cinnamon.
This can be made in a ramekin. Just press the crust into the ramekin and top with the persimmon mixture. If you'd prefer a warm pie, just bake it in a 350 degree F (175 degree C) oven for 15 minutes.