Finely chop the onion, garlic and chilli.
Heat the oil in a large saucepan and gently sauté the chopped vegetables until soft.
Meanwhile, peel and chop the sweet potatoes, red pepper and carrot. Add these to the pot, stir for a minute, then add the spices & chipotle paste and/or tomato purée.
Add the chopped tomatoes and just enough water to cover the vegetables. Season to taste.
Bring to the boil, cover, turn down the heat and cook for 20 minutes until the vegetables are tender.
Turn off the heat. Add the coriander leaves. Season to taste, then pulse with a stick blender until you get a thick, smooth sauce. You can now chill or freeze the sauce.
In another saucepan, cook the pasta according to the packet instructions.
Finely chop the spring onions.
Drain the pasta, then put it back into the pan.
Reheat the sauce, if needed.
Ladle some sauce onto the pasta, add the spring onion bits and olives. Toss well, then serve with coriander leaves and freshly ground pepper scattered on top.
Use the remaining sauce for other meals.