Preheat Oven:Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan with nonstick spray or butter and line with parchment paper if desired for easy removal.
Make Batter:In a large bowl, combine brownie mix, eggs, oil, and water. Stir until well combined. Gently fold in chocolate chips if using.
Layer Batter and Fudge:Pour half the batter into the prepared loaf pan. Drizzle half the hot fudge sauce over the batter. Use a knife or skewer to swirl slightly. Add the remaining batter on top, then drizzle and swirl in the rest of the hot fudge.
Bake:Bake for 45–55 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs. (Avoid overbaking for a fudgier texture.)
Cool and Serve:Let the bread cool in the pan for 15–20 minutes before transferring to a wire rack. Slice and serve warm or at room temperature. Drizzle with additional hot fudge if desired.