Soak the Oats: Place the oat flakes into a mixing bowl and pour hot water over them. Stir gently and let the oats soak for about 5 minutes to soften.
Prepare Wet Ingredients: In another bowl, whisk together the eggs, sweetener, and vanilla extract until the mixture is smooth and well combined.
Combine: After the oats have soaked and softened, add the egg mixture to the oats. Stir until everything is evenly incorporated.
Bake: Preheat the oven to 350°F (175°C). Pour the oat mixture into a greased baking dish and spread it out evenly. Bake for 25–30 minutes, or until the cake is set and the top is slightly golden.
Cool and Serve: Allow the cake to cool for a few minutes before cutting it into squares. Serve warm or at room temperature.