Rinse the quinoa under cold water and cook it according to package instructions.
While the quinoa is cooking, prepare the vegetables by dicing the tomatoes, cucumber, bell pepper, and red onion.
In a large bowl, combine the cooked quinoa, diced vegetables, and chopped parsley.
Drizzle the olive oil and lemon juice over the mixture, and season with salt and pepper.
Toss everything together gently until well mixed, and let the salad sit for at least 10 minutes before serving.
Serve chilled or at room temperature, garnished with extra parsley if desired.