Preheat oven to 350 degrees F. In a large roasting tin, add the squash, carrots, potatoes and leeks. Drizzle over 2 tablespoons of the olive oil and toss well. Roast for 45 minutes, turning the vegetables half way through cooking.
In a large stainless steel pot set over medium high heat, add the remaining olive oil, garlic, ginger, cumin, coriander, cinnamon and bay leaves. Stir until sizzling, about 1-2 minutes. Add the vegetables and stir well to completely coat in the spices. Add the vegetable stock and bring to a simmer. Reduce heat to low, cover and leave to simmer for about 15 minutes.
Remove soup from heat and remove the bay leaves. Blend in batches in your blender. Return soup to pot and simmer over a low heat for a few minutes. Season with black pepper.
Serve topped with Greek yoghurt and fresh mint leaves.
*A note on times provided: appliances vary, any prep and/or cook times provided are estimates only.