Preheat the oven to 350 degrees F.

Mix walnuts, raisins and chocolate chips in a bowl and blend in lemon zest.

Whip egg whites with cream of tartar in a mixer with whipping attachment, starting at slow speed for a minute then increase speed to medium-high until the soft-peak stage. Turn speed to slow and add sugar gradually.

Turn whipped egg whites into a large wide bowl.

Sift flour on top of egg whites little bit at a time and fold it in along with part of the nut-fruit-chocolate chip mixture. Continue with flour and nut mixture, folding gently until all is added and totally incorporated (avoid overworking that tends to deflate the egg white foam).

Pour into parchment- or foil-lined bread pan or well-greased tube pan with removable bottom.

Bake in preheated oven for 35 to 40 minutes or until skewer comes out clean.