Set a rack in the lower third of the oven and preheat to 350 . Toast the walnuts for 15 to 20 minutes, until they become somewhat fragrant and lightly browned. Cool completely.Brush a bundt pan with oil and dust with flour.
When the walnuts are completely cooled, place in the workbowl of a food processor along with 1/4 cup of the sugar and the orange zest. Pulse a few times to grind to a very fine dice, not too powdery. Reserve one cup of the walnut-orange zest mixture.
In a large bowl, sift together the flour, Rumford Baking Powder, baking soda, cinnamon, nutmeg and salt. Whisk the eggs, walnut and vegetable oil, honey and the remaining 3/4 cup sugar. Make a well in the center of the flour mixture and whisk in the egg mixture along with the boiling water. Stir in the 2 cups of walnut-orange zest mixture. Pour batter into prepared bundt pan.
Bake for about 50 minutes or until the top springs back when pressed with a finger. Cool on a rack for about 20 minutes and unmold on the rack for glazing.
While the cake is baking, bring the brown sugar, rum and orange juice to a low boil and, stirring often, boil for about 8 minutes.While the cake is still warm, set the rack above a plate and brush on the glaze about 3 times over the course of 15 minutes, allowing syrup to be absorbed. Return any glaze that runs onto the plate back to the cake. Wipe the plate clean and press the reserved one cup walnut-orange zest mixture evenly over the cake. Press any walnuts that fall onto the plate back on the cake. Cool completely and serve.