Photograph: Tara Fisher
Wash the lentils under cold running water, then put them in a large pan with the bay leaf, thyme and a generous pinch of salt. Cover the lentils with at least double their volume of boiling water and cook for 15-20 minutes, or until tender.
Meanwhile, make the vinaigrette by whizzing the dill (including the stalks) in a blender with all the other ingredients.
Use a mandolin or a sharp knife to thinly slice the beetroot. Drain the lentils and discard the bay leaf and thyme.
To assemble, arrange the salad leaves and beetroot slices on a platter, scatter over the lentils and crumble over the goats' cheese. Drizzle with the vinaigrette and a little extra-virgin olive oil; finish with a sprinkling of salt and pepper and the cress.
Get ahead: cook the lentils up to a few hours ahead. Make the vinaigrette up to an hour ahead.
Kitchen secret: if time's tight you could always use a pouch of ready-cooked lentils instead.
This recipe is adapted from The Little Paris Kitchen by Rachel Khoo (Michael Joseph, £20).