Toast quinoa in a dry pan over medium-high heat until golden and fragrant, about 5 minutes.
Add water, bring to a boil, then reduce heat, cover and simmer for 15 minutes until tender. Let rest covered for 5 minutes, then fluff with a fork and cool to room temperature.
Mix olive oil, lemon juice, salt and pepper to make the dressing.
Combine parsley, mint, green onions, and tomatoes in a large bowl. Add cooled quinoa and pour dressing over top.
Gently stir to combine and adjust seasoning if needed. Serve at room temperature or chilled.