Prepare the Oven and Pan
Preheat your oven to 350°F (175°C). Grease an 8.5 × 4.5-inch or 9 × 5-inch loaf pan, or line it with a loaf pan liner.Mash the Bananas
Place the ripe bananas in a large mixing bowl and mash them until mostly smooth. A few small banana pieces are perfectly fine and can add extra flavor throughout the loaf.Make the Batter
Add the eggs, melted butter, and yellow cake mix to the mashed bananas. Stir gently until everything is just combined.Be careful not to overmix. Overmixing can make the finished bread denser instead of soft and tender.Fill the Loaf Pan
Pour the batter into your prepared loaf pan. Use a spatula to gently smooth the top so the batter is evenly distributed.Bake
Place the pan in the preheated oven and bake for approximately 55–60 minutes.Start checking toward the end of the baking time. Insert a toothpick into the center of the loaf. If it comes out clean or with a few moist crumbs, the banana bread is ready.