Heat oil in a large saucepan over medium-high heat. Add onion and eggplant; sauté, stirring frequently, until vegetables are lightly browned.
Add pumpkin and zucchini. Stir in chilli powder, cumin and garlic. Pour in canned tomatoes with their juice. Add salt and pepper, to taste. Heat to boiling, breaking up tomatoes with a wooden spoon. Cover and simmer 15 minutes, stirring occasionally, until pumpkin is just tender. Check occasionally, adding water, if needed, to prevent vegetables from sticking.
Preheat oven to 180ºC. To make the guacamole, halve and stone the avocado, scoop flesh into a bowl and mash with lime juice. To make salsa, combine tomato, red onion and coriander in a small bowl. Set guacamole and salsa aside.
Put taco shells on a baking tray; warm 3 to 4 minutes in the oven. Transfer shells to serving plates. Fill with eggplant mixture and top with guacamole, yogurt and salsa. Garnish with lime wedges and coriander.
DID YOU KNOW
...that when tomatoes were introduced into Europe, they were regarded with suspicion and thought to have aphrodisiac properties? Nutritionists now know that ‘love apples’, as these fruits were called, do have benefits for the heart, but not in the romantic sense.