Heat oven to 200C/180C fan/gas 6. Grate the garlic and ginger into a large roasting dish. Add the lentils, onions, cauliflower, turmeric and cumin seeds. Pour over 500ml boiling water and give everything a good mix. Rub the chicken thighs with the oil, curry powder and a pinch of salt and pepper. Nestle these into the lentils, then cook in the oven for 40 mins until the lentils and chicken are cooked through.
Add the spinach and tomatoes to the dish, remove the chicken and return to the oven briefly for a couple of mins until the spinach has wilted. Season to taste. Serve with the lemon wedges and yogurt.