Preheat your oven to 350°F (175°C) and grease an 8-inch square baking dish with butter or nonstick spray.

In a large mixing bowl, combine chopped rhubarb with brown sugar, vanilla extract, and lemon juice. Stir until fully coated.

Pour the filled rhubarb mixture evenly into the prepared baking dish.

In a separate bowl, whisk together Bisquick, melted butter, and milk until just combined.

Using fingers or a spoon, break the Bisquick dough into small pieces and scatter them over the rhubarb filling.

Bake in the preheated oven for 40-45 minutes until the topping is golden brown and filling bubbles.

Remove from the oven, allow to cool for 10 minutes, then serve warm, optionally with whipped cream or vanilla ice cream.