Preheat the oven to 350F. In a bowl, mix all-purpose flour, baking powder, baking soda and salt. Stir with a whisk. Cream together soft unsalted butter and sugar together in a bowl. Add lemon juice, zest and sour cream in with sugar mix everything.
Incorporate eggs on low and mix again. In portions, add flour dry ingredient mixture to the bowl. This will make a thick dough.
Grate zucchini over a few paper towels, fold and gently press down to remove most of the moisture, add that and poppy seeds into your butter mix. Use spatula to gently fold in and incorporate.
Line loaf pan with parchment paper or spray with non stick spray. Pour the batter in it. Cover with foil and bake for 20 minutes. Then bake without foil for another 20 minutes.
Make syrup from poppy seeds, water, sugar, lemon juice. Heat until sugar dissolves and let cool. Remove the bread from the oven - it turns out quite tall with a dense crust.
Transfer the zucchini bread to a wire rack and pour over the syrup, being careful not to soak the top too much. Let the syrup dry on top (5 minutes) and you can cut the bread.