Preheat the oven to 180°C.
Trim courgettes and cut into five equal-sized slices.
Scoop out a small amount of flesh from the top of each slice using a melon baller.
Place slices on a tray, drizzle with oil, season, and roast for 12 minutes until soft.
Heat 15ml of oil in a pan and fry chopped onions for 5 minutes until caramelized.
Heat remaining 15ml of oil in a separate pan and fry mushrooms with herbs until soft.
Drain any excess liquid from the mushroom mixture.
Blend cooked onions, mushrooms, herbs, and cream cheese in a food processor until smooth.
Transfer the mousse into a piping bag.
Pipe the mousse into the roasted courgette hollows.
Top each with an asparagus tip and sprinkle with crushed hazelnuts to serve.