Preheat the oven to 180C / 360F.
Peel and dice the sweet potatoes into small pieces.
Tip the sweet potato into a large pot of water. Bring to a boil, then reduce the heat to a light simmer. Cook for 15 minutes, or until fork tender.
Transfer the sweet potatoes to a food processor along with the non-dairy milk, olive oil, ginger powder, sage and salt and black pepper (if using). Blend for ten seconds or so, until creamy.
Make the oat topping by adding the oats, pistachios, maple syrup, olive oil, herbs and garlic powder to a food processor and pulse blending to a fine powder (it will be slightly sticky due to the oil and maple syrup).
Spoon the sweet potato into a baking dish, and sprinkle on the oat topping. Add a further few pistachio nuts on top. Bake for 10-12 minutes, in the middle or lower half of the oven. Keep an eye on it for any signs of burning in the last few minutes of cook time!
Sprinkle with some fresh sage leaves, then serve immediately and enjoy!