Preheat the oven to 425°F. Line a baking sheet with foil and brush an 8x11-inch baking dish, or similar, with olive oil.
Use a fork to poke a few holes into the sweet potatoes. Place on the baking sheet and roast until very tender, about 60 minutes.
Make the crumble topping: In a food processor, place the oats, pecans, walnuts, garlic, maple syrup, olive oil, thyme, rosemary, and salt and pulse until just combined. Remove and set aside.
Scoop the cooked sweet potato flesh out of the skins and place in a food processor. Add the olive oil, almond milk, ginger, salt, and several grinds of pepper and process to combine. Spread the mixture into the baking dish.
Sprinkle with the crumble topping, additional nuts, and sage. Drizzle with olive oil and bake 20 minutes or until the topping is browned and crisp.