Preheat the oven to 200 degrees F.
Mix the rhubarb, pecans, sugar, flour, lemon zest and cinnamon together in a bowl.
Use your fingers to push the rhubarb mixture into each apple, dividing the mix evenly.
Add a blob of butter to the top of each and sprinkle with more sugar. Bake in the oven until the apples are tender, about 25 minutes. Serve warm with whipped cream or ice cream.