Healthy kumara and turkey burgers

Ingredients

• 1 large kumara (orange sweet potato) (500g), unpeeled (see tip)
• cooking-oil spray
• 1/3 cup (25g) quinoa flakes
• 1/4 cup (60ml) milk
• 400 grams minced (ground) free-range turkey or chicken
• 1 small zucchini (90g), grated coarsely
• 1 small purple carrot (70g), grated coarsely
• 1 small red onion (100g), grated coarsely
• 1 tablespoon finely chopped fresh flat-leaf parsley
• 2 tablespoons olive oil
• 1 large tomato (220g), sliced thinly
• 100 grams trimmed watercress
• 1 small red onion (100g), extra, sliced thinly
• 1 tablespoon sesame seeds, toasted
• Green tahini
• 1/4 cup (70g) tahini
• 2 tablespoons fresh flat-leaf parsley leaves
• 2 tablespoons lemon juice
• 1 tablespoon olive oil
• 1 small clove garlic, crushed