Wash the vegetables well and do not peel them if they are organic.
Cut the squash and potatoes into medium-sized cubes (about 1.5/2 cm square).
Coarsely chop the onion into strips. Preheat your oven to 210°C.
You can pre-cook the vegetables in the steam (15 minutes for the potatoes and 12 minutes for the pumpkin with the onion), to reduce the cooking time in the oven. You can also skip this step and cook for longer in the oven, or even pan-fry the whole thing.
Next, place the vegetables in a casserole dish and drizzle generously with olive oil. Add the spices and mix well to coat your vegetables with oil and spices.
Place the dish in the oven.
Halfway through cooking, add the olives and mix well so that the vegetables are evenly cooked.
After 25 minutes, check the cooking of the vegetables with the tip of a knife: it should sink in easily and the flesh of the vegetables should be tender. If necessary, extend the cooking time by about ten minutes.