Preheat the oven to 200°C/fan 180°C/gas mark 6. Add the asparagus to a roasting tray, then toss with 1 tbsp olive oil and season well. Transfer to the oven and roast for 10-15 minutes until tender. Meanwhile, place the pancetta on a separate baking tray and cook in the oven for 15 minutes, or until crispy.
Whisk together the tahini, lemon juice, garlic and remaining olive oil, gradually adding 50ml water until you have a loose consistency. Add an extra 1-2 tbsp water if you want it runnier.
Toss together the puy lentils, cherry tomatoes and asparagus. Season to taste and plate up, topped with the pancetta and drizzled with the dressing.