Preheat your oven to 350℉/176℃ and line a 9-inch square baking pan with parchment paper.
Add your dates and water to a high-speed blender and process until smooth to make date syrup. Set it aside.
Whisk all the dry ingredients in a large bowl. Then add the applesauce, lemon zest, lemon juice, and 1.5 cups worth (NOT more) of the date syrup you just made. Stir until combined. (Reserve the remaining date syrup for the glaze.)
Transfer the batter to your baking dish and bake for 25-30 minutes, until a toothpick inserted in the middle comes out clean. Remove it from the oven and let it cool for at least 10 minutes. Then transfer the loaf to a cutting board or cooling rack to completely cool.
Meanwhile, add 2 tablespoons of lemon juice to the remaining date syrup and mix. (Taste it and add more lemon juice, if preferred.) Then drizzle the glaze on your lemon loaf and let it rest for a few minutes to set before slicing into 16 squares.
Notes
Use active baking powder. Oat and rice flour are denser than white flour and need a little extra to rise nicely. If your baking powder is very old or has been open in your pantry for 6+ months, it may start to lose its effectiveness. Test it before using it if you're unsure.
If you don't have a high-speed blender or your dates are very dry, soak them first for 15 minutes in hot water, and then drain them. This will soften the dates, making them easier to blend.
Don't dump all the date syrup into the loaf. Make sure to follow the instructions carefully. Use only 1.5 cups of your syrup, and reserve the rest for the glaze.
To maximize the juice you get from a lemon, you may soak whole lemons in a bowl of hot water for 30 minutes, or microwave them for 10-20 seconds. You may also roll lemons on a countertop with your hands to get the juices flowing.
For the glaze. Mix 2 tablespoons of lemon juice into the date syrup and taste the mixture. Add more lemon juice until the desired lemony flavour is reached.
The spices are subtle in flavour, since the lemon is the star of this dessert. For stronger spice, double the cinnamon, ginger, and nutmeg called for in the recipe.
Cool your loaf to room temperature before glazing. Once glazed, let it rest for a few minutes so it slightly hardens before slicing.