Preheat an oven to 350°F
To make the crust, in a food processor, pulse the flour, walnuts, brown sugar and butter on low speed until combined, 30 seconds to 1 minute. Press the crust into the bottom of a 9-inch springform pan. Bake until lightly browned, 10 to 12 minutes. Cool on a wire rack. Reduce the oven to 300°F.
To make the filling, in the bowl of a cleaned out food processor, pulse the cream cheese and brown sugar until smooth, 1 to 2 minutes. Add the pumpkin puree, vanilla and spices and beat until smooth, about 1 minute. Add the eggs one at a time, pulsing after each addition.
Wrap a double layer of aluminum foil around the bottom and sides of the springform pan. Add the filling and smooth the top. Place in the center of a roasting pan. Pour hot water into the roasting pan to reach halfway up the sides of the springform pan. Bake until the cheesecake is firm but jiggles slightly in the center, 45 minutes to 1 hour. Let cool in the water bath before topping with the meringue. The cheesecake can be refrigerated overnight.
To make the meringue, in a saucepan, bring 1 inch of water to a simmer. Place the egg whites, brown sugar, agave and vanilla bean seeds in a stand mixer bowl and set over but not touching the simmering water. Whisk until the sugar is dissolved and the mixture is hot, about 2 minutes. Place the bowl on the mixer and beat with the whisk attachment on high speed until the meringue cools to room temperature and stiff peaks form, 5 to 6 minutes.
Lightly pat the cheesecake with a paper towel to remove moisture. Mound the meringue on top, using a pastry spatula to spread it to the edges, it should be quite tall. Using a spoon, create mountains and swoops of meringue around the surface. Lightly brown with a kitchen torch. Serve immediately or refrigerate for up to 6 hours. Serves 8 to 12.