In a mixing bowl, mash the bananas with a fork until you reach a nice puree with as little chunks as possible. Add the yogourt, flax seeds and baking soda and mix well. Set aside for 5 minutes.
Mix in the oil, sugar and vanilla. Add the flour, baking powder and salt and mix just enough to combine. Fold in the nuts and chocolate chips.
Pour the mixture into an oiled loaf pan and bake for 1h, rotating the pan at 180 (half-turn) after 30 minutes. The bread is ready when a toothpick comes out clean.
If your bananas are too big, the bread won't cook well *You can use any oil or even better runny natural peanut butter). **You can keep at room temperature for 1 or 2 days but if you plan on keeping it longer, than store in the fridge.