Combine onions and peppers in a small bowl and add vinegar and olive oil. Mix well and set aside to marinate for 30 minutes.
In the mean time, combine the mixed grains with 2cups of water . Bring to a boil, lower the heat, cover and cook until all the water is absorbed and grains are tender, about 20~30 minutes. If using regular (not pre-cooked) grains, then adjust the water quantity and cooking time.
Combine cooked grains, marinated veggies, olives, chickpeas, fresh herbs, olive oil, red wine vinegar, salt and pepper. Mix gently, taste and adjust the seasoning. Serve warm or at room temperature.