Preheat the oven to 180°C/350°F (fan-forced).
Make the marinade by grinding the mustard seeds using a mortar and pestle (or high speed blender) until the seeds are almost ground. Add the remaining marinade ingredients and mix until combined.
Break the cauliflower into florets and add to a bowl with the carrots. Add the mustard marinade and combine thoroughly so that all the vegetables are coated.
Spread the vegetables out on a baking tray in a single layer and roast for 40 mins, or until the vegetables are tender and just beginning to brown.
Meanwhile, make the dressing. Place all of the ingredients into a jar and shake to combine.
Place the cooked lentils and kale in a serving dish. Pour the dressing over the lentils and kale and toss well. Sit at room temperature whilst the vegetables continue to cook.
When the vegetables are ready, toss them through the lentils/ kale and serve immediately.
You can also make this ahead. Store in the fridge and allow to come down to room temperature prior to serving.