1 Preheat the oven to 200 ̊C, gas mark 6. Pierce the sweet potatoes all over with a fork. Bake for about 1 hour 30 minutes, until the centres are soft, then set aside.
2. Lower the oven to 160 ̊C, gas mark 2. Toss the kale, walnuts and whole garlic cloves with 1 tbsp oil; roast for 10-12 minutes, until crisp.
3 Once the potatoes are cool enough to handle, halve them and scoop out the middles, keeping the skin intact (leave a little flesh in the shells so that they hold their shape). Beat the flesh with the remaining 1⁄2 tbsp oil, a squeeze of lemon juice and most of the salad cheese; season. Pile back into 4 of the halved sweet potato skins (discard the other two) and scatter over the remaining cheese. Pop back in the oven to warm through.
4. Squeeze the garlic cloves out of their skins into the small bowl of a food processor. Add the kale and walnuts, mint and basil, and pulse until roughly chopped. Stir through the lemon zest, season, then scatter over the sweet potatoes and serve.