Place the rack in the center of the oven. Preheat the oven to 350° F.

If rhubarb is green, peel it. Chop off any parts containing leaves, those are poisonous. Chop rhubarb in about ¼ inch pieces. If the stalks are large, slice them in half longways before chopping.

Wash, hull and dry strawberries. Dice into pieces just slightly larger than the rhubarb.

In a medium mixing bowl, combine rhubarb, strawberries, ⅓ cup sugar, lemon juice and lemon zest. Stir to coat fruit evenly. Spoon into a shallow 1 ½ quart casserole dish.

In a separate bowl, whisk together flour, remaining ½ cup sugar, cinnamon and salt. Cut in the butter with a pastry blender until the mixture comes together and is crumbly and homogenous. There should be no visible pieces of butter left. It should be clumpy. You can also do this in a food processor or stand mixer. Sprinkle evenly over the fruit mixture.

Bake at 350°F for about 50 minutes or until the mixture is hot and bubbly and the topping is golden brown.