In a saucepan, combine chopped rhubarb, granulated sugar, water, and lemon juice. Cook over medium heat until the rhubarb is soft and the mixture thickens, about 10-15 minutes.

In a separate bowl, mix gelatin powder with 1 cup of water and let it bloom for 5 minutes. In a saucepan, combine the remaining sugar and cornstarch with 1 cup of water. Cook over medium heat, stirring constantly until it thickens.

Once the gelatin has bloomed, add it to the rhubarb mixture and stir well. Then, gradually add the thickened sugar and cornstarch mixture, whisking continuously until smooth.

Pour the mixture into a greased square baking dish and let it cool at room temperature for several hours or until set.

Once set, dust a clean surface with a mixture of powdered sugar and cornstarch. Cut the Turkish delight into squares and coat each piece with the sugar-cornstarch mixture to prevent sticking.