Preheat the oven to 375°F.

Add the olive oil and flaxseed to a large mixing bowl and whisk until well combined.

Add the pumpkin and brown sugar and whisk again.

To a second mixing bowl, add the flour, oats, baking powder, cinnamon, ginger, allspice, and salt. Stir until well combined.

Slowly blend the oatmeal mixture into the pumpkin mixture, stirring just until the batter is well combined. Fold in the chocolate chunks.

Coat an 8-inch X 4-inch baking pan with a very thin layer of olive oil. Pour the batter into the pan, spreading and smoothing the top with a small spatula or table knife, ensuring the corners are filled in and the surface is perfectly smooth and even.

Press several additional chocolate chunks into the top surface of the batter (optional).

Bake for about 38-43 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool, about 10-15 minutes.

Run a table knife along every side of the cake, ensuring cake doesn't stick to the sides of the pan. Turn the pan over onto a tray or cutting board to remove the cake from the pan. Flip the cake so it's right side up. Slice and serve.