Steam or blanch the asparagus, broccolini and snow peas for 2 - 3 minutes or until they are just tender and still bright green. Rinse under cold water and drain. Set aside.
Put the lentils in a large pot, add the stock and add 250ml of water and bring to the boil. Reduce the heat and simmer for 20 minutes or until the lentils are tender. Drain the lentils and reserve 60ml of the stock.
Return the lentils to the pot, add the oil, garlic, mustard, lemon juice, reserved stock and steamed or blanched vegetables. Cook over a low heat for 2 minutes or just until warmed through.
Remove from the heat and stir through the basil and spinach. Season with cracked black pepper.