Preheat the oven to 400F/200C.
Peel and de-seed the squash and cut into roughly bite-sized pieces. Remove the ends from the Brussel sprouts and cut them in half length-wise, or in quarters if larger. Remove the outer 'leaf' from them as well. Peel and roughly chop the onion.
Toss the squash, sprouts and onion in 1tbsp of the oil and lay in a single layer in a baking dish/baking sheet. Sprinkle over the salt and roast for approx 30min until the squash is tender and all vegetables are just browning.
Meanwhile, have a piece of parchment paper ready to put the pecans on. Then toast the pecans for a couple minutes in a dry skillet/frying pan until you can start to smell their slight nuttiness. Remove from the heat and add the maple syrup. Quickly toss so all the pecans are coated then tip out onto the parchment, making sure the buts are separated. Leave to cool.
Whisk together the lemon juice, pomegranate syrup and remaining 2tbsp olive oil for the dressing.
Once the squash and sprouts have cooked, add the pecans, broken up if you prefer, pomegranate seeds and drizzle over the dressing (you may not want all of it). Best served warm.