Roast the pistachios for 15 min at 180°C, chop them finely and put them in a bowl.
For the dressing, finely chop the fronds of the fennel and add them to the oil, juice of half a lemon, white wine vinegar, pepper, and salt, and mix.
Slice the fennel into thin slices using a mandoline.
Peel the melon, cut it in half, remove the seeds, and slice it into super thin slices also using a mandoline.
Place the fennel and melon in a nice large bowl, add the ricotta and basil on top.
Finish with the dressing and if you like it spicy, you can add some chili flakes!
Tips
If there is no more green foliage on your fennel, you can also use dill.