Preheat the oven to 180°C.
Toss cauliflower florets with olive oil, salt, and pepper on a baking tray.
Roast cauliflower for 20 minutes until golden-brown and tender.
Heat ghee or oil in a saucepan and fry onion for 3 minutes until translucent.
Add ginger, mustard seeds, curry leaves, turmeric, fenugreek, chillies, and chilli powder.
Cook for 3 minutes until seeds pop, then stir in the potatoes to coat.
Add tomatoes, spinach, sugar, and 55ml of water.
Simmer for 20 minutes while stirring occasionally.
Stir in roasted cauliflower and season with salt, pepper, and lemon juice.
Discard whole chillies and serve with steamed basmati rice.