Heat oven to 325°F for nonstick pan. Grease bottom only of pan (use paper baking cups for cupcakes).
Beat Cake Mix, water, melted butter, vanilla, egg, chia seeds and lemon zest in large bowl on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan.
Bake for 35 minutes or until toothpick inserted in center comes out clean.