Preheat the oven to 170°C. Lightly grease mini bundt cake molds. I used 12 80ml bundt cake molds.
In a stand mixer beat together sugar, eggs and oil.
In a bowl mix flour, vanilla seeds, ground ginger, ground cinnamon and baking powder.
Add flour mix to the egg mixture spoon by spoon.
Add yogurt, chopped lemon balm and mix until the mixture is smooth and even.
Add rhubarb and use a spatula or a big spoon to mix it in.
Use an ice cream scoop to fill the molds to about 3/4 full.
Bake in the preheated oven for about 25 minutes, until the toothpick comes out clean. Let cool in the molds
In a mortar bash the lemon balm with 1 TBSP of lemon juice to get out as much lemon balm juice as you can. Use a fine sieve or gauze to squeeze out the liquid. Discard the solids.
Add 1 TBSP lemon juice and the lemon balm liquid to the icing sugar and whisk until smooth.
When bundt cakes are cooled to room temperature, remove them from molds and decorate with lemon drizzle.