Season beef with 1 tsp of salt, dash of black pepper. In a small pan, saute beef quickly for 2 minutes on medium high heat.
In a medium pot, bring 3 quart of water to boil. Add sliced tomatoes, cook for 5 minutes or until tomatoes have became soft.
Add mango and cook for another 5 minutes. After that, add cooked beef and dill in hot boiling pot, cook for 1 minute. Adjust seasoning with salt and sugar.
Turn off the heat after 1 minute. Garnish with Vietnamese coriander. Serve when soup is hot.