Blend tomatoes, 1/2 onion and 3 cloves of garlic; strain into a bowl.
Heat oil in a medium saucepan over medium heat. Stir in the strained tomato juice and simmer for a few minutes until it changes to a darker colour. Add chicken stock and bring to the boil.
Combine the minced chicken, 3 diced tomatoes, diced onion, mint, oregano, egg, rice, salt and pepper in a large bowl. Mix well and use your hands to form golf ball-sized meatballs.
Using a ladle, gently lower the meatballs into the simmering soup. Simmer until the meatballs float, then add the sliced courgette, carrots and chayote squash. Taste for seasoning; cover and cook on low until vegetables are tender.
Chayote squash taste a little like courgettes. They are available in Mexican and West Indian grocers.