Place all the yogurt sauce ingredients in a small mixing bowl, and stir until combined. Refrigerate until ready to serve.
To make the cauliflower curry:
Preheat the grill to roughly 400ºF (204ºC). In a very large mixing bowl, place the cauliflower, potatoes, white onions, tomatoes, peas, and chickpeas. Drizzle coconut oil over the top of the veggies, and stir until coated. Add the curry powder and a pinch of salt and pepper, and stir again until evenly coated.
Tear out 4 pieces of aluminum foil that are 12 x 18 inches (30 x 46 cm), and lay them out. Divide the curry cauliflower mixture between the 4 sheets, place it in the middle. Fold the two long sides in toward the middle, and fold the seam together until it hits the filling. Fold the two short sides in, twice, to seal the ends.
Place each packet on the grill and cook for 7 minutes, flip them over and grill for an additional 7 minutes. Carefully, open one packet slightly, and poke the cauliflower and potatoes to see if they are tender. If not, cook until they are.
Once cooked through, place the packets on a cooling rack for 5 minutes before opening and serving.
When the packets are opened, squeeze lemon juice over each one, and top with salt and pepper. Serve packets alongside yogurt sauce and enjoy.