Preheat oven to 350 degrees F. Spray a half baking sheet pan (9x13 inches) with cooking spray and line with parchment paper.

Make the cake. Whip together the eggs with granulated sugar and brown sugar in a large bowl until doubled in volume, about 4 minutes. It should be creamy and thick.

Slowly add the oil and honey, mixing constantly until well combined for 1 minute. Add the vanilla and stir to combine.

Stir together the flour with cinnamon, ginger, nutmeg, baking powder, baking soda, and salt in a medium bowl. Add half of the flour to the batter, stirring just until combined. Add the buttermilk and mix until combined. Add the remaining flour mixture, stirring just until combined. Stir in the chopped pears.

Pour the cake batter into the prepared baking sheet, spreading the batter evenly. Bake the cake for 30 minutes or until a toothpick inserted in the center comes out clean. Remove from the oven and let cool completely on a wire rack.

Meanwhile, make the chocolate tahini frosting. Beat the softened butter with tahini until creamy, about 2 minutes. Slowly add the powdered sugar until it's fully incorporated. Add the cocoa powder and beat until combined. Add the vanilla and milk and beat for another 30 seconds or until smooth and creamy.

Spread the frosting on the cake in an even layer. Sprinkle sesame seeds on top and garnish with sliced pears if desired.