Are these courgettes overcooked, if so how can I avoid it?
I think the biggest issue is you're baking them instead of roasting them. In order to roast them, you'll need a much higher temperature. 230c or 450f is about right. As Joe pointed out, the pieces are a bit thin for roasting. Spears or large chunks will serve you better. Roast them skin side down and brushing on a little olive oil will prevent the skins from drying out.