Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line baking tray with baking paper.
Wash the sweet potatoes well. Peel the onions. Cut both into slices. Rinse and drain the chickpeas. Wash thyme, shake dry. Put everything in a large bowl. Sprinkle with oil, season with salt and pepper. Mix well and spread on the baking tray.
Bake in a hot oven for about 30 minutes.
The oven vegetables taste great as a main course, e.g. with mashed potatoes or bread and dips like sour cream or hummus. As a side dish, prepare only half the amount and serve with poultry, steaks, chops or fish fillets.