Put a dry frying pan over a medium heat. Add ½ tsp each coriander, cumin and fennel seeds. Toast for 2-3 mins till they start to pop. Tip into a pestle and mortar (or use a bowl and jam jar bottom) and finely grind them.
Zest both the oranges. Juice 1 of them. Add the juice and half the zest to a large bowl. Whisk in the toasted spices, ½ tsp cinnamon, a pinch of harissa, 2 tbsp olive oil and a pinch of salt and pepper.
Drain and rinse the lentils. Tip into the dressing bowl. Finely chop the mint and mix into the lentils.
Tear the watercress, discarding any tough stems. Arrange on a platter or plates. Scatter the dressed lentils over, folding them into the watercress.
Slice the top and bottom from the remaining orange. Set on a board, slice the skin off and slice into rounds. Tuck the orange into the salad.
Crush the cashews a little. Warm a dry frying pan over a medium heat. Lightly toast the cashews, shaking the pan so they don’t burn. Season with salt. Scatter over the salad. Drizzle 1 tbsp olive oil and top with the rest of the orange zest.