Peel and cut potatoes into 1-inch pieces. Trim and peel carrots. Cut them in half lengthways and then into 1-inch pieces. Peel and cut the sweet potatoes into 1-inch rounds. Peel onions. Halve them and cut each half into quarters.
Add all veggies to a large rimmed, lined baking sheet. Spread them so they are not touching each other. Drizzle with a bit of olive oil and sprinkle with a dash of salt and pepper.
Roast in the oven for 20 minutes.
Prepare the dressing by mixing garlic, ginger, soy sauce, mirin, sake, miso paste and sesame oil in a bowl.
Remove veggies from the oven. Drizzle the dressing over the veggies and pop back in the oven to roast for a further 20-25 minutes until the veggies are tender, golden and starting to crisp around the edges.
Remove from the oven. Scatter with spring onion and coriander. Sprinkle sesame seeds and Shichimi Togarashi. Serve immediately.
The roasted veggies can be stored in the fridge in a lidded air-tight container for up to 3 days.