Preheat oven to 200C. Place pumpkin in a roasting pan, brush with oil and roast until golden and tender (20-25 minutes).
Meanwhile, cook lentils in a saucepan of salted boiling water until tender, adding corn in the last 5 minutes (about 20 minutes). Drain.
For nut-milk dressing, process pepitas, nuts, garlic, vinegar, oil and 200ml water in a blender. Season to taste and stand to infuse for an hour, then squeeze the dressing through a piece of muslin into a bowl (optional).
Combine pumpkin, lentils, corn, herbs, spring onion and pepitas in a bowl and season to taste. Transfer to serving bowls, drizzle with nut-milk dressing and serve.