Peel the mangoes and cut the flesh off the pit, cut flesh into 1/4-inch dice. Place in a bowl with the tomatoes, onion and jalapeno and gently mix.
In a separate bowl, mix the yogurt and garam masala. Fold the yogurt into the fruit, season with the salt, and gently fold in the cilantro.
Cover and refrigerate at least 1 hour, but no longer than 2. Stir well before serving.