Preheat the oven to gas 7, 220°C, fan 200°C.
Boil the potatoes for 12-15 mins until tender; drain.
Tip into a shallow roasting tin and use the back of a fork or spoon to press down on each potato and crush it a little.
Drizzle over 1½ tbsp olive oil, add the thyme leaves and toss to coat. Season and add the lemon wedges.
Roast for 20 mins, then stir in the lentils. Roast for 5-10 mins until the potatoes are golden and crispy.
In a large bowl, whisk together the lemon zest and juice, mustard, sugar, 2 tbsp olive oil and chopped dill; season.
Tip in the warm potatoes, lemon wedges and lentils; toss well to coat.
Spoon into a serving bowl and garnish with the remaining dill leaves.
