Slice the loaf of low-carb cinnamon bread into 12 thick Texas toast–style slices. If you prefer smaller portions, cut into 24 regular slices, but note that this will change the serving size to 2 slices per portion.
Whisk together the melted butter and brown sugar substitute until combined. Spread about 2 tablespoons of this mixture over the bottom of the prepared baking dish.
In a medium bowl, whisk together the almond milk, eggs, vanilla extract, and a sprinkle of cinnamon until the mixture is smooth.
Arrange half of the bread slices in a single layer in the prepared baking dish. Spoon or drizzle half of the butter–sweetener mixture over the bread, then pour half of the egg mixture on top.
Repeat with a second layer of the remaining bread slices, butter–sweetener mixture, and egg mixture, ensuring the bread is well coated.
Cover the dish tightly with foil and refrigerate overnight or for at least 8 hours, to allow the bread to soak up the custard.
Bake The Dish:
When ready to bake, preheat the oven to 350°F. Remove the dish from the fridge and let it sit at room temperature for 15 minutes.
Bake, covered, for 20 minutes. Remove the foil and continue baking for another 20–25 minutes, until the top is golden brown and the center is set.
Make The Glaze:
While the French toast bake is finishing, prepare the glaze. Whisk together the softened cream cheese, almond milk, vanilla extract, and powdered sweetener until smooth.
Finish And Serve:
Remove the French toast bake from the oven. Drizzle the glaze over the dish while it's hot.
Slice and serve immediately with sugar-free syrup if desired.