Preheat oven to 250 degrees F (120 degrees C). Grease and flour 2 9x5-inch loaf pans.Advertisement
Stir cake mix and water together in a large bowl; add vegetable oil, pecans, pudding mix, eggs, poppy seeds, vanilla extract. Stir until just combined. Pour batter into the prepared pans.
Bake in the preheated oven for 15 minutes. Increase temperature to 300 degrees F (150 degrees C) and bake until a toothpick inserted in the center of a loaf comes out clean, about 45 more minutes.