Place the peach slices, water, and lemon juice in a large saucepan and simmer for 10 minutes, stirring occasionally. While the peaches are simmering, get out two bowls for the dry/wet ingredients used to make the topping.
To make the topping:
Combine dry ingredients in a medium bowl (almond flour, baking powder, salt, ground cinnamon, and ground nutmeg if using.) Set aside.
In a separate bowl, whisk together the rest of the topping ingredients - melted butter (or coconut oil), 3 tablespoons of the maple syrup, 1 egg and ¼ teaspoon vanilla extract. Set aside.
Bringing it all together:
When the peaches are done simmering, place them in an 8x8 baking dish. Sprinkle the peaches with 1 tablespoon arrowroot flour (or tapioca flour/cornstarch) and drizzle in 1 tablespoon maple syrup and 1/2 teaspoon vanilla extract. Stir together until everything is combined.
Next, add the wet ingredients for the topping to the bowl that contains the dry ingredients for the topping. Stir together until well combined.
Scoop spoonfuls of the topping over the peach mixture. As mentioned above, it's best to leave a little space between the spoonfuls to allow some heat to escape from the peach mixture during baking. This prevents the peaches and topping from "steaming" and becoming soggy.
After you have spooned the batter over the peaches, smooth it out a little bit with a spatula.
Bake for 25 - 30 minutes, or until deep golden brown on top.