Preheat oven to 350°F, and prepare a loaf pan by greasing lightly with butter, or lining with parchment paper.
In a mixing bowl, measure the flour, baking powder, baking soda, salt, and ginger. Mix together to blend well, and set aside for now.
In a second bowl, beat the butter until smooth, and add the sugar, continuing to beat until the texture is light and fluffy.
Beat the eggs lightly before adding them to the butter/sugar, mixing until just incorporated.
Mash the bananas with a fork in a third bowl, mix as you add the yogourt, lemon juice and zest.
Add the banana mixture to the egg mixture first, blending until combined.
Take half the wet ingredients, and add them to the dry flour mix, stirring to blend, but only just.
Then add the remaining wet ingredients, taking care not to over mix. If you do, the result will be a very dense loaf.
Pour the batter into the loaf pan, and place thin slices of lemon on top.
Sprinkle with the coarse sugar, and pop in the oven.
Bake for 55 to 65 minutes, until a clean knife inserted into the center comes out clean.
Allow the loaf to cool for about 20 minutes before tapping it out of the pan.
Keeps in the fridge, covered, for about a week.