Peel the sweet potatoes and cut into bite-sized cubes, cut the cauliflower into florets and dice the stalk. Put the sweet potatoes and stalk in boiling salted water for 10 minutes, then add the florets for another 8 minutes, then drain the water.
Mix the spices with the lemon juice, then stir in the yogurt. Season well with salt. Roast the garlic cloves in oil.
Mix the garlic, vegetables and sauce together and let it steep for at least 30 minutes, then season again to taste. Fold in fresh chopped parsley.