Preheat oven to 220C (430F).
Start by soaking the uncooked lentils in plenty of water for half an hour. This step is not essential, but will speed up the cooking process and improve digestion of the lentils.
Drain and rinse the lentils, then put them in a saucepan with plenty of cold water. Bring to a simmer and cook for about 15 minutes, until tender but with a little bite. Drain the lentils and rinse them under cold water to stop the cooking process. If you didn't soak the lentils, allow 20-30 minutes cooking time.
Roast the vegetables while the lentils are cooking. Give the potatoes a five minute head start: put them in a roasting tray, spray or brush with a little olive oil and pop them in the oven. When five minutes is up, add the cauliflower and red onions, spray or brush with more olive oil, then sprinkle evenly with ground turmeric, coriander and salt. Roast for 20 minutes, giving everything a shake and a little more oil half way through cooking, if needed.
Mix the cooked (or canned) lentils with parsley, lemon zest and segments, olive oil and salt.
To make the dressing, put all ingredients into a jar with a lid and shake to combine. Taste and adjust seasoning if needed.
To serve, assemble leafy greens, roasted vegetables and lentils on a serving platter or in individual bowls. Top with a generous drizzle of dressing and enjoy.