Toss the zucchini with cinnamon, lemon juice, and apple flavoring in a small bowl, choosing the flavoring amount to suit your taste, then leave it aside while preparing the dough. The pieces should look evenly coated and smell of cinnamon and apple.
Whisk the almond flour, protein powder, monkfruit sweetener, baking powder, xanthan gum, and salt together in a medium bowl. An even mixture helps distribute the leavening and binders throughout the dough.
Work the melted butter, nut milk, sour cream, water, and egg into the dry mixture until fully incorporated. Expect a thick mixture that holds a scoop rather than pouring freely.
Fold the seasoned zucchini and its bowl juices through the dough. Look for an even scattering of pieces without concentrated pockets of cinnamon.
Heat lard over medium heat in a small nonstick skillet, using enough to reach almost halfway up the fritters, then add approximately 1/4-cup scoops of dough, gently swirl the fat around their sides, and turn after about 3–5 minutes before browning the second side. The underside should be firm and golden before turning, with both sides golden when finished.
Lift the fritters out of the skillet and transfer them to paper towels or a wire rack to cool. A rack lets steam escape underneath and helps preserve the bottom crust.
Stir the confectioners sweetener, heavy whipping cream, and vanilla together in a small bowl, microwaving for 20 seconds only if the glaze needs thinning. The mixture should flow smoothly enough for dipping or drizzling.
Coat the tops with glaze by dipping or drizzling, then leave the fritters on a wire rack until the coating sets. The glaze should settle into a thin coating rather than collect in thick puddles.