Rinse 1 cup of quinoa under cold water. In a medium pot, combine quinoa with 2 cups of water or vegetable broth. Bring to a boil, then reduce heat to low, cover, and let simmer for about 15 minutes.
Chop the mixed vegetables into bite-sized pieces.
Spread the vegetables on a baking sheet and drizzle with olive oil, minced garlic, salt, and pepper. Roast for 20-25 minutes, stirring halfway through.
Fluff the cooked quinoa with a fork in a large bowl. Add the roasted vegetables and the lemon juice, then toss everything together until combined.
Serve warm or at room temperature, or cool and store in an airtight container in the fridge for up to 4 days.
Notes
Let the salad sit for at least 15 minutes before serving to help the flavors meld together.