Very little oil in the bottom of the shallow pan, to start the onions first; when they begin to brown, add the zuchini, still with the glass lid.
The cooking is quite fast if the lid seals properly (sometimes a little too much is added, which lifts the lid and lets the heat escape) it's possible to forget this kind of dish for a long time without serious consequences, quite the opposite, the overcooked dish caramelises as it simmers without burning, long after exceeding its normal cooking time it will remain a delight.
