Heat oven to 350°F. Grease bottom only of 3 (5 3/4 x 3 inch) mini loaf pans (I use these) or one large pan (9 x 5 x 2 3/4 inch); set side.
Combine all ingredients except Nutella in a bowl. Beat at medium speed, scraping bowl often, until well mixed.
Heat Nutella in a small bowl, microwave for 10-15 seconds, being careful not to overheat.
Spoon half of pumpkin batter into prepared pans. Spoon half of Nutella over pumpkin mixture. Swirl gently with a knife. Spoon remaining pumpkin batter over top. Repeat with Nutella, swirling gently. Bake 25-35 minutes for mini loaves or 50-60 minutes for 1 large loaf. A toothpick inserted in center comes out clean. Cool 10 minutes; remove from pan. Cool completely on a wire rack.