Cut the stalks off of the beets as well as the narrow part of the beet. Wrap the beets in foil and place on a baking sheet. Cook for 50 minutes.
While the beets are cooking in a sauté pan heat the oil on medium heat. Add the onions and cook until translucent. Add the mushrooms and cook until soft. Once the mushrooms are tender add the kale, garlic, salt and pepper and cook until the kale was wilted. Remove form the heat and set aside.
Reduce the heat to 375°F, 190°C, or gas mark 5.
Roll out the puff pastry and place on the baking sheet. Top with the kale mixture, followed by the beets, then the goat cheese and then the walnuts. Overlap the remaining dough over the edge of the filling. Baked for 30 minutes or until the pastry becomes golden brown.