Heat the oven to 160°C (140° fan) 325°F gas 3. Line 2 baking trays with non-stick baking paper.
Cut the pumpkin flesh into chips and place on the baking tray. Bake for 20 minutes, then remove and drain on absorbent kitchen paper.
Increase the oven temperature to to 200°C (180° fan) 400°F gas 6.
Cut the potatoes into chips and cook in a pan of boiling salted water for 5 minutes, then drain well.
Put the pumpkin and potatoes into a large shallow bowl and toss with the salt. Spray lightly with the olive oil spray and toss, using your hands.
Place on the baking trays and spray with olive oil spray. Cook for about 20 minutes, until the vegetables are browned and tender. Sprinkle with salt.
For the olive dip: crush the garlic with a little sea salt and make a paste with a little of the lemon juice.
Stir in the yoghurt, olives and remaining lemon juice and salt to taste. Spoon into a serving bowl. Garnish with dill.