Preheat oven to 350F; line the inside of an 8 1/2 by 4 1/2-inch metal loaf pan with 2 pieces of parchment paper so it hangs over all 4 sides and spray the corners with coconut or avocado oil.
Whisk together the almond flour, flaxseed meal, erythritol, tapioca starch, oat fiber, cinnamon, salt, baking soda, and nutmeg in a large bowl.
Whisk together the slightly cooled butter or coconut oil, eggs, cream/water mixture, vinegar, vanilla, and stevia glycerite in a medium bowl.
Add the wet ingredients to the dry all at once and stir until combined, being careful not to over-mix. Fold in the zucchini and walnuts.
Immediately pour the batter into the prepared pan and bake until a toothpick inserted into the center comes out clean, about 1 hour, 15 minutes.
Once it’s done cooking, turn off the oven and let the bread sit in the hot oven for 10 minutes before removing to a wire rack to cool completely.
Store any leftovers wrapped in the fridge for up to 5 days.