Preheat the oven to 180˚C (350˚F). Clean and slice the pumpkin and place on a baking tray. Sprinkle with salt and pepper and bake for about 20 minutes. Shake the pan occasionally. Rinse and drain the lentils.
Combine the dressing ingredients and mix. Season to taste with salt and pepper. Arrange the arugula on a flat plate and top with the roasted pumpkin and lentils. Drizzle with dressing and garnish with sesame seeds and scallions.