1-Getting started with rhubarb oatmeal bars: First, preheat your oven to 350ºF to ensure even baking. In a mixing bowl, combine the oats, flour, and brown sugar, then pour in the melted butter and stir until the mixture is crumbly and evenly combined.

2-Preparing the base and layering: Next, press two-thirds of the oat mixture into an 8×8 inch baking pan to form the base. Spread the rhubarb evenly on top for that fresh, tangy layer. Sprinkle the remaining oat mixture over the rhubarb to complete the layers.

3-Baking and cooling: Now, bake in the oven for about 30 minutes, or until the top is browned and the rhubarb is cooked through. Once done, let the bars cool for at least 15 minutes before serving to hold their shape. These bars yield about 12 servings and can be enjoyed warm or cold, making them a versatile treat for any time of day.