Preheat oven to 350°F (175°C). Grease and line a 9x9 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.

Prepare the crust: In a medium bowl, combine the flour, sugar, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Press the mixture evenly into the bottom of the prepared pan.

Bake the crust for 15 minutes until lightly golden brown. Remove from the oven and set aside while preparing the other layers.

Prepare the rhubarb topping: In a small saucepan, combine the chopped rhubarb, sugar, cornstarch, and lemon zest. Cook over medium heat, stirring constantly, until the rhubarb softens slightly and the mixture thickens (about 5-7 minutes). Remove from heat and let cool slightly.

Prepare the cheesecake filling: In a large bowl, beat the softened cream cheese until smooth. Gradually beat in the sugar until fully incorporated. Beat in the eggs one at a time, mixing just until combined. Stir in the vanilla extract.

Assemble and bake: Pour the cream cheese mixture evenly over the warm crust. Gently dollop spoonfuls of the cooled rhubarb mixture over the top of the cheesecake layer. Use a knife or skewer to gently swirl the rhubarb into the cream cheese.

Bake for 35-40 minutes, or until the edges are set and the center is mostly set (a slight jiggle is okay). Allow to cool completely on a wire rack before chilling in the refrigerator for at least 4 hours, or preferably overnight, before slicing into squares.