1. Heat the olive oil in the bottom of a Dutch oven. Add the peeled and chopped onions.
2. Cook them slowly over low heat for 15 minutes. If necessary, add a little water to prevent sticking.
3. Preheat your oven to 350°F.
4. Meanwhile, peel the zucchini and sweet potatoes. Leave a strip of skin on every other slice of zucchini.
5. Cut them roughly (according to your taste... I prefer zucchini in not too thin slices and fairly large pieces of potatoes).
6. The onions should have a caramel color.
7. Then add the zucchini, sweet potatoes, and the raisins that have been soaked in tea.
8. Season with spices according to your taste, whether sweet or savory... Personally, I add 1 teaspoon of cinnamon, 1/2 teaspoon of coriander, a pinch of sweet paprika, and salt and pepper to taste. Tip: taste it! You can always adjust the seasoning at the end of cooking.
9. Add a little water to the Dutch oven (not too much!), cover it with perforated aluminum foil to cook the dish in a tajine style (it's even better if you have one of those special tajine pans).
10. Place it in the oven and let it simmer for at least 1 hour and 30 minutes.
11. Serve hot, accompanied by couscous grains (which can be cooked with 1 teaspoon of cinnamon to add flavor - personally, at this point, I prefer the sweet-savory contrast, so I add salt to my grains - it's up to you!).