For the dressing: Stir together the water, fish sauce and sugar until the sugar dissolves.
For the salad: Combine the trout, dried shrimp, shallots, mango and mint in a salad bowl. Add 1/4 cup of the dressing and mix well. Garnish with the peanuts and chiles and drizzle with the garlic oil. Serve the remaining dressing on the side for drizzling.