Tomato Egg Drop Soup (with frozen tomatoes!!)

Name: Tomato Egg Drop Soup (with frozen tomatoes!!)
Prep time: 10 min
Cook time: 5 min
Total time: 15 min
Cuisine: Chinese
Ingredients: 2 large tomatoes - about 300g ((or 3 small tomatoes)); 3 medium eggs ((or 2 large eggs)); 2 tbsp cooking oil ((I used vegetable oil) ); 4 cups chicken/vegetable stock - 32oz ((or water)); 3 tbsp cornstarch; 3 tbsp cold water; 1 - 1½ tsp salt ((gradually add to your taste)); ½ tsp white pepper ((or black pepper, gradually add to your taste)); 1 tsp sesame oil ((optional)); 1 green onion ((or cilantro))