Combine pineapple, carrot, and water in a microwave-safe bowl. Cook in the microwave until carrots and pineapple are partially softened, 1 to 2 minutes.
Stir almond milk, oats, cinnamon, and ginger into the bowl. Cook in the microwave for 1 minute. Stir. Continue microwaving in 30-second intervals, stirring after each interval, until oats are tender, 1 to 2 minutes more. Top with walnuts.