In a pot over medium heat, combine the soy milk, rice, sugar, zero-calorie sweetener, and salt. Stir to combine.

Bring the mixture to a boil over high heat, stirring occasionally to prevent sticking. Once boiling, reduce the heat to low and simmer uncovered for about 25-30 minutes, stirring often, until the rice is soft and the mixture has thickened.

Let cool for 5 minutes, then whisk in the protein powder until fully dissolved and no lumps remain.

Transfer the mixture to a baking dish or individual containers. Press plastic wrap directly onto the surface to prevent a skin from forming, then refrigerate for at least 2 hours or overnight.

Before serving, remove the plastic wrap and sprinkle cinnamon on top. Serve.