Make the cake: Preheat the oven to 350 degrees F. Lightly butter two 9-inch-round cake pans; line the bottoms with parchment paper.
Whisk the flour, baking soda, baking powder, cinnamon, ginger, cardamom, allspice and salt in a large bowl; set aside. Combine the pumpkin, sugar, orange zest and vanilla in a stand mixer fitted with the paddle attachment and beat on medium speed until smooth, about 1 minute. Add the eggs, one at a time, beating until each one is incorporated. With the mixer running, add the vegetable oil in a steady stream. Add the flour mixture and mix just until incorporated. Divide the batter between the 2 prepared pans; lightly tap the pans on the counter to distribute the batter.
Transfer the pans to the oven and bake until the cakes begin pulling away from the pans and the centers spring back when lightly pressed, about 30 minutes. Transfer to a rack and let cool 10 minutes in the pans, then unmold onto the rack and let cool completely.
Meanwhile, make the filling: Combine the sugar and 1/4 cup water in a large deep saucepan over medium-high heat; bring to a simmer and cook, without stirring, until deep amber, about 8 minutes. Carefully whisk in the cream and cook, whisking, until smooth. Add the corn syrup and bring to a boil, then reduce the heat to medium low and cook, whisking occasionally, until the sauce thickens slightly and coats the back of a spoon, 40 to 50 minutes. Remove from the heat; whisk in the butter, chocolate, vanilla and salt until smooth. Let cool completely, then fold in the pecans. Cover and refrigerate until firm but spreadable, about 1 hour.
Assemble the cake: Cut each cake in half horizontally with a serrated knife to make 4 layers. Put 1 layer on a platter; spread one-third of the pecan filling on top. Layer the remaining cakes and filling on top, ending with cake. Refrigerate until set, about 1 hour.
Make the glaze: Combine the chocolate, cocoa powder, butter and honey in a microwave-safe bowl. Cover with plastic wrap and microwave 1 minute; uncover and whisk until smooth. Let cool to room temperature, then spread on the cake, letting the excess drip down the sides. Refrigerate until the glaze sets, about 10 minutes.