Preheat the oven to 350 degrees. Grease a medium-sized loaf pan.

Mash the bananas with stevia and lemon juice. Set aside.

Sift the dry ingredients together in a bowl. Beat the oil and egg together in another bowl until creamy.

Beat in the buttermilk and the vanilla. Stir in the mashed bananas. Fold the dry ingredients into the wet ingredients, add the nuts, and stir just until moist.

Bake for 50 minutes or until a toothpick inserted in the center comes out clean.

Turn the loaf out to cool on a rack.