Combine water, quinoa, and 3 Onion Dip Mix in a Multipurpose Pot over medium-high heat. Bring to a boil, reduce heat, and simmer, stirring occasionally, for about 15 min, until water is absorbed. Remove from heat and let stand 5 min.
Turn into a large bowl and stir in vinaigrette, tomatoes, olives, and tuna. Season to taste. Serve warm or at room temperature.