1. Wash the zucchini and cut them into slices about 3 mm thick.
2. Brown them in a pan with a little olive oil, salt, and pepper.
3. Preheat the oven to 210 °C (425 °F).
4. Prepare the crumble:
Cut the butter into small cubes in a bowl, add the sugar and then the oat flakes, mix everything with your fingertips and refrigerate.
5. Prepare the pesto:
Peel the garlic, then wash and dry the basil. Put them in a blender, add the pine nuts, parmesan cheese, and olive oil. Blend everything well until you get a sort of paste.
6. Mix the zucchini with the pesto, then arrange them in a gratin dish. Sprinkle the oat crumble on top and bake for about 30 minutes.