Preheat the oven to 350℉. Lightly grease a 9 x 13-inch metal baking pan with nonstick cooking spray. You can also line with parchment or foil and then grease for easy cleanup.
In a large bowl, mix together dry cake ingredients—flour, cinnamon, pumpkin pie spice, nutmeg, baking soda, salt, and baking powder. Set aside.
Whisk the oil (melted and cooled if using coconut oil), packed dark brown sugar, maple syrup, and heavy cream in a medium bowl until smooth. Add the vanilla and pumpkin, dabbing the pumpkin with a paper towel if too wet. Avoid adding extra pumpkin to prevent the cake from becoming too moist. Whisk until smooth.
Pour wet ingredients into dry. Mix until just combined, be careful not to overmix the batter. Spread the batter evenly in the prepared pan.
In a medium bowl, whisk together the streusel dry ingredients—flour, brown sugar, cinnamon, and salt. Add the butter and mix with a pastry blender or your fingers until the streusel is evenly combined and forms small clumps. Sprinkle the streusel mixture over the cake batter.
Bake until the edges begin to pull away from the sides of the pan and a toothpick inserted in the center comes out clean or with a few moist crumbs attached—about 35 to 40 minutes. Cool completely in the pan before icing.
Combine all the glaze ingredients in a small bowl. Start with 2 tablespoons milk and add more as needed. Whisk with a fork until smooth. Drizzle over the individual pieces and enjoy!
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Notes
Storage: Store leftover Pumpkin Coffee Cake in an airtight container at room temperature for 1-2 days or in the fridge for up to 5 days. For longer storage, freeze individual slices wrapped in plastic for up to 3 months.