Heat oven to 350°F and lightly grease a standard loaf pan, including the corners.

Mix water, egg, and muffin mix in a bowl just until moistened; batter should be thick and slightly lumpy.

Fold in poppy seeds from the mix until evenly combined.

Pour batter into the prepared pan and spread it evenly to the edges.

Spoon cherry pie filling on top and gently swirl with a knife to create visible ribbons.

Bake 50–55 minutes until golden brown and a toothpick comes out with a few moist crumbs.

Cool in pan for 5 minutes, loosen edges, then transfer to a rack and cool completely before slicing.