Preheat the oven to 350 degrees F.
Heat a grill pan over medium-high heat; spray with cooking spray. Add the plums, cut-side down, and cook for 1 to 2 minutes, just until charred. Remove from the heat.
In a bowl, combine the flour, 4 tablespoons of the turbinado sugar, and the butter, lemon zest and cinnamon. Mix with your hands and squeeze gently to create dime-size clumps.
In four 4-ounce Mason jars, add 1 tablespoon of the crumble; then add a plum half, grilled-side up. Score the plums in a criss-cross pattern¿this will allow the flavors to seep into the plums and make them easier to eat later. Fill each pit divot with 1 teaspoon bourbon and sprinkle with the remaining 2 tablespoons turbinado sugar. Divide the remaining crumble evenly between the jars. Set the jars in an 8-by-8-inch baking dish; pour 1/4 cup water into the baking dish.
Bake on the center rack until the plums are soft and the crumble is golden brown, 20 to 25 minutes. Let cool.
Garnish each serving with a tablespoon of whipped cream. Serve.