Turn on oven to 375°F. Toss sweet potatoes with a drizzle of oil, salt and pepper. Spread out in a single layer on a baking sheet and set a timer for 25 minutes.
Set a large saucepan with 3.5 cups of water (7 cups for 4 servings) on to boil. Crumble in the stock cube. Once boiling, reduce heat to low to keep the stock warm.
Heat large skillet or pot over medium with 1 tbsp. of oil (2 tbsp. for 4 servings). Once the skillet is hot, add the shallots and garlic. Cook for 1 minute until the mixture has softened. Add the rice and deglaze the pan with the white cooking wine. Once the wine is mostly absorbed, add a ladle or two of the warm vegetable stock to the skillet, and stir well.
The risotto will need to cook for about 18-20 minutes, over this period of time you will slowly add more and more of the stock each time the rice gets dry (about every 1-2 minutes). Give it a good stir each time you add more stock. You will have used almost all of the stock by the time the 20 minutes is up. If you have extra, that's okay there is no need to be exact about the amount of stock you add. You want the risotto to be a nice texture at the end, without being dry or too thick. Keep tasting rice to test doneness.
Wash and roughly chop the sage and rosemary leaves and set aside. Toast the walnuts in a small skillet over medium heat for about 5 minutes or until fragrant.
Stir in the green peas, parmesan and chopped herbs. Remove sweet potato from the oven and smash with a fork. Stir into risotto and divide between serving dishes. Roughly chop or tear the arugula. Top risotto with arugula, crumble goat cheese and sprinkle toasted walnuts. Enjoy!