Preheat your oven to 375°F (190°C). Grease a medium-sized baking dish.
In a saucepan over medium heat, cook zucchini with lemon juice and water for 8–10 minutes until softened.
Add erythritol, cinnamon, nutmeg, salt, glucomannan, and vanilla to the zucchini. Stir and cook 2 more minutes.
Transfer the zucchini mixture to the greased baking dish.
In a bowl, mix almond flour, coconut flour, melted butter, pecans, brown sugar substitute, and cinnamon until crumbly.
Sprinkle the topping evenly over the zucchini mixture.
Bake for 25–30 minutes, or until golden and bubbly.
Cool slightly before serving. Serve warm with keto-friendly ice cream if you’re feeling fancy.