Mushroom Shakshuka ​​​​​​(Baked eggs in rich tomato sauce)

• 1 small brown onion, finely chopped
• 1 tbsp extra virgin olive oil
• 200 g cup mushrooms, sliced
• 1 tbsp tomato paste
• 1 tbsp harissa paste
• 4 cloves garlic, crushed
• 1.5 tsp ground cumin
• 0.5 tsp dried chilli flakes
• 1.5 tsp salt
• 800 g diced tomatoes (tin)
• 4 free-range eggs
• 1 handful of fresh herbs to serve
• 0.5 tsp Za’atar (optional)