Preheat the oven to 390°F (200°C). If using convection/fan-forced, preheat to 350°F (180°C).
Place the cauliflower florets, cauliflower leaves, and sliced onion into a large roasting pan. Add the garlic, ginger, oil, garam masala, curry powder, turmeric, salt, and cayenne (if using). Toss with your hands until evenly coated.
Roast for 20 minutes, uncovered, until the vegetables begin to soften and brown lightly.
Carefully remove the tray from the oven. Add the chickpeas, coconut milk, diced tomatoes, tomato paste, almond butter, and bouillon powder. Stir everything together gently in the pan (it will be hot—use a spoon or spatula to avoid burns).
Return the tray to the oven and roast for another 20–25 minutes, or until the cauliflower is fork-tender and the sauce is thickened slightly.
Remove from the oven and let it sit for 5 minutes to settle before serving.