Preheat your oven to 350°F (175°C) and allow at least 15 minutes for it to fully come to temperature. Spray your 9x13 inch baking pan or Bundt pan generously with non-stick cooking spray, making sure to coat all corners and ridges thoroughly.
Add the entire can of cherry pie filling, 3 large eggs, and the full box of chocolate cake mix into a large mixing bowl. Make sure all three ingredients are in the bowl before you begin mixing.
Using an electric hand mixer on medium speed, beat the ingredients together for about 2 minutes until fully combined with no dry streaks of cake mix remaining. If mixing by hand, stir vigorously for 3-4 minutes, scraping the bottom and sides of the bowl; do not over-mix.
Pour the thick batter into the prepared pan and use a spatula to spread it into an even layer, reaching the corners and edges. Tap the pan gently on the counter two or three times to level the batter and release any air bubbles.
Bake on the center rack for 40-45 minutes for a 9x13 pan, or 45-50 minutes for a Bundt pan, until a toothpick inserted in the center comes out clean or with just a few moist crumbs. If the top browns too quickly before the center is set, loosely tent with aluminum foil for the remaining bake time.
Remove the cake from the oven and place it on a wire cooling rack; let it cool in the pan for at least 15 minutes before slicing or inverting. For a Bundt pan, run a thin spatula around all edges before inverting, then allow to cool completely before glazing.
Whisk together 1 cup powdered sugar, 2 tablespoons cocoa powder, and 2-3 tablespoons milk in a small bowl until smooth and pourable. Drizzle over the fully cooled cake and allow the glaze to set for about 10 minutes before slicing.
Slice into 12-15 portions and serve with whipped cream, a scoop of vanilla ice cream, or a dusting of powdered sugar. Store leftovers covered at room temperature for up to 2 days or refrigerated for up to 4-5 days.