Preheat the oven to 350℉. Line an 8x8" glass baking pan with parchment paper.
In a small bowl, combine the dairy-free milk and lemon juice. Mix and set aside.
In a large mixing bowl, whisk together the gluten-free flour, sugar, baking soda, baking powder, salt, and cinnamon.
Add the oil, egg, and milk mixture. Stir until a smooth batter forms. Stir in the rhubarb until evenly distributed in the batter.
Pour the batter in the 8x8" pan and spread it into an even layer. In a small bowl, combine the topping ingredients. Sprinkle the sugar and almonds over top the cake.
Bake for 45-50 minutes. A toothpick inserted into the center of the cake should come out clean and the cake should be puffy.
Let the cake for at least 1 hour before slicing and serving. Store cooled leftovers in an airtight container at room temperature for 4-5 days.