Step 1Place the lentils in a large saucepan and fill with water to cover by 2 inches. Simmer until tender, about 20 minutes, then drain the lentils and transfer them to a medium bowl. Season the lentils with one-fourth teaspoon salt and several grinds of pepper and drizzle over about 1 tablespoon of vinegar. Taste the lentils, and adjust the seasoning or vinegar, or both, if desired. Set aside the lentils to cool, stirring occasionally.
Step 2In a large saucepan, combine the rinsed quinoa with 2 cups water and bring to a boil over high heat. Cover the pot and reduce heat to a gentle simmer, cooking until the grain is soft and translucent, about 15 to 20 minutes. The water should be absorbed; if not entirely absorbed, drain any excess. Remove from heat and fluff the quinoa with a fork. Transfer the quinoa to a large bowl, drizzle about 2 tablespoons of oil on the grain and stir gently.
Step 3In a small bowl, whisk together the garlic, one-fourth cup vinegar, one-half cup olive oil, one-fourth teaspoon salt and one-eighth teaspoon pepper. Taste and add additional seasoning if desired.
Step 4Stir the cooled lentils in with the quinoa in the large bowl. Stir in the dressing, then cover and chill the salad for at least 1 hour.
Step 5Just before serving, stir in the mint, parsley and tomatoes and check the seasoning. Drizzle with a bit more vinegar and oil.