Preheat the oven to 375 degrees Fahrenheit.
Cut the acorn squash in half and save the seeds to roast later (like pumpkin seeds). Cut each half into quarters, use a sharp knife to peel the pieces away from their skin and arrange in a roasting tray or sheet pan lined with parchment.
Peel beets with a vegetable peeler and halve (small ones) or quarter (large ones) them. You want your pieces of beet to all be about the same size. Place them in the roasting tray. Cut the onion into sixths and tuck between the other vegetables. Remove the fronds from the fennel (if they came with it) and cut each bulb into sixths. Spread around the roasting tray. Drizzle the vegetables with a little olive oil.
Use a mortar and pestle to crush the coriander with a good pinch (1/4-1/2 teaspoon) sea salt and black pepper. Sprinkle over the vegetables and toss to coat.
Roast for about 40 minutes, tossing the vegetables about halfway through. The onions and fennel should be soft and golden and just starting to caramelize. The beets should be easily pierced with a fork. Remove from the oven and allow to cool slightly.
Meanwhile, make the dressing. Combine all the ingredients in a jar with an airtight lid and shake until well mixed.
Toss dressing, roasted vegetables, mint, parsley, pomegranate and feta (if using) to serve.