Preheat oven to 350F.
Mix the flax egg and set aside.
Oil a regular-sized loaf pan and then line it with parchment paper so you can easily pull out the loaf when cooled.
In a large bowl, whisk the dry ingredients (flour, powders, salt, cinnamon, nutmeg, sugar, raisins, and walnuts). In another large bowl, combine the wet ingredients (flax egg, shredded zucchini, lemon zest and juice, maple syrup, milk).
Add wet ingredients to dry and stir until just mixed. Be careful not to overmix the batter as spelt flour is delicate.
Spoon the batter into prepared loaf pan and spread out evenly. Prepare the cinnamon streusel and then sprinkle on top. Bake for about 45-60 minutes at 350F or until toothpick comes out clean and the loaf gently springs back when pressed.