Pre-heat your oven to 350F with a rack in the middle.
Grease a loaf pan with butter and line it with a strip of parchment paper.
In a medium mixing bowl, combine the sugar with the zest of the two lemons (reserve the lemon juice for the glaze).
Add in the yogurt, eggs and vanilla extract. Mix to combine.
In a large mixing bowl, combine spelt flour, poppyseed, salt and baking powder. Combine into the wet ingredients until just incorporated. Finally add in oil until just incorporated. The batter should look smooth and glossy.
Transfer batter to prepared pan and bake for 50-55 minutes, until golden and a knife inserted in the center comes out clean. Transfer the cake to a cooling rack.
Combine the powdered sugar with 2 tablespoons of lemon juice (adding more if needed), until smooth and pourable. With a toothpick poke holes in the top of the bread. Brush the loaf with the glaze and set aside to cool and harden.