Zesty za'atar roast chicken

Ingredients

• Field & Flower 1.75kg Whole Chicken
• 1 lemon (halved with one half cut into slices)
• 2 onions, roughly chopped into large pieces
• 3 sprigs of thyme
• 250g Greek yogurt
• 1 lemon, zested and juiced
• 2 garlic gloves, crushed
• 3 tbsp olive oil
• 2 tbsp white sesame seeds, toasted
• 2 tbsp sumac (optional)
• 1 tbsp dried thyme
• 1 tbsp ground coriander
• 2 tbsp dried oregano
• 2 tsp ground cumin