Place the chopped, pitted cherries into a small ceramic bowl.

Add the granulated sugar and fresh orange zest to the cherries. Stir well to combine and set aside, allowing the natural sugars to draw out the fruit juices (maceration).

In the bowl of a food processor, combine the all-purpose flour, chopped walnuts, and brown sugar. Pulse briefly to integrate the dry ingredients.

Pour the melted butter directly into the food processor.

Pulse the machine 2 to 3 more times until the mixture clumps together into a coarse, heavy streusel. Set aside.

Preheat the oven to 350°F. Generously coat a 9-inch square baking pan with vegetable oil spray or butter.

In a medium bowl, whisk together the flour, ground cinnamon, baking powder, baking soda, and kosher salt.

In the bowl of a stand mixer, cream the softened butter and granulated sugar together on medium-high speed until pale and highly fluffy.

Reduce the mixer speed to low and add the eggs one at a time, ensuring each is fully incorporated before adding the next.

Gradually add the dry flour mixture to the wet ingredients, mixing only until just combined to prevent overworking the gluten.

Spread exactly half of the thick cake batter into an even layer at the bottom of the prepared baking pan.

Drain any excess liquid from the macerated cherries. Spoon the fruit evenly over the base layer of batter.

Dollop the remaining cake batter over the cherries. Use an offset spatula to gently spread the batter (it does not need to be perfectly smooth).

Run a butter knife through the layers in a figure-eight motion to gently swirl the fruit and batter together.

Scatter the prepared walnut streusel heavily and evenly over the top of the cake.

Bake in the preheated oven for 55 to 60 minutes, or until the streusel is deeply golden brown and a wooden tester inserted into the center comes out perfectly clean. Allow to cool before slicing.