Place the pecans on a cookie sheet and bake at 325 degrees for 5-7 minutes or until lightly toasted and fragrant. Allow the pecans to cool completely, then finely chop them, and set them aside. In a bowl, sift together 2 C. flour, 1/4 C. sugar, baking powder, 1/4 t. cinnamon, and salt. In a small measuring cup, whisk together the water and oil. Using your fingers, mix the water-oil mixture into the flour mixture, adding additional flour as needed to form a soft ball of dough. Cover and set aside for 10 minutes to allow the dough to rest.
In a small bowl, stir together the pumpkin puree, remaining 1/2 C. sugar, remaining 1t.cinnamon, ginger, allspice, and nutmeg, and set aside.
Spray a non-stick cookie sheet with vegetable cooking spray and set aside. Transfer the rested dough to a floured work surface; roll it out to 1/16 inch thickness, and cut the dough into 24 3-inch circles or squares.
To shape each pastry: place a rounded teaspoonful of the filling on one half of each circle (or square). Sprinkle 1/4 t. reserved chopped pecans over the filling, fold the other half of the dough over the filling to enclose it, gently press the edges together with your fingers, and then go around the edges with a fork to seal them together.
Repeat the assembly procedure for the remaining circles of dough. Using a spatula, transfer the filled pastries to the prepared cookie sheet. Bake at 375 degrees for 18-20 minutes or until golden brown. Allow the pastries to cool on the cookie sheet for several minutes before transferring them to a rack to cool completely. Store in an airtight container when completely cool.