Pick leaves of thyme sprigs and add to oil, together with the lemon zest, and garlic in a small saucepan.
Warm on a very gentle heat. Leave to infuse for 6 minutes.
Take off heat and leave to cool in a large bowl.
Discard the garlic.
Put the squash, walnuts, and lemon juice in the oil with 1/3 teaspoon salt and a good amount of coarse ground black pepper. Then, massage for a minute or so. Stir in basil and serve at once.