Add yogurt, eggs, and oil and fold the mixture together.
Line and grease four small (12cm) loaf tins.
Pour half the batter into another bowl. Into the first bowl, add the most of the chocolate chips and the grated orange zest.
Pour this batter into two loaf tins. Top with the remaining chocolate chips.
The chocolate chip cakes will take about 30 minutes to bake. Test with a toothpick: when comes out cleanly, the cake is done. Depending on your oven, you may need to cover the top with foil to stop the top burning.
In the second bowl, stir in the lemon zest.
Divide half of the remaining batter between two loaf tins. Sprinkle on most of the berries. Spread the remaining batter on top.
By filling the tins this way, you avoid having the berries sink to the bottom and having the juice from the frozen berries "bleed" in to the batter.
The cakes baked with frozen berries will take longer. Test after 35 minutes baking, but be prepared for another 5 minutes.
Allow to cool for a few minutes before removing the cakes from the loaf tins.