Finely slice or shred the fennel, cabbage, onion and radishes. Deseed and remove the vein of the chilli, then cut it into thin slices( if used). Chop the fennel fronds, set aside.
Scatter all the shredded vegetables into a large mixing bowl.
Mix the dressing, season with salt & pepper. Taste, and adjust it to your liking.
Pour the dressing over the salad, toss well, then rest for 10-15 minutes for the vegetables to soften.
Just before serving, peel the avocado, remove the stone, and cut the flesh into chunks.
Add the avocado pieces, together with the chopped herbs and fennel fronds, to the salad and toss gently.
Serve immediately.