Heat the 1 tablespoon of olive oil in a medium skillet. Add the onion and cook for 3 minutes.
Add the Cubanelle and mushrooms. cook another 3 minutes.
Add the garlic and cook 2 minutes more. Remove from heat and allow to cool.
Put the cooked quinoa in a large mixing bowl. Add the roasted peppers, artichoke hearts, sun-dried tomatoes and olives and toss to combine.
Add the cooled onion mixture to the bowl and toss once again.
In a small jar with a lid add all of the dressing ingredients (except salt and pepper). Close tightly and shake until the ingredients are emulsified.
Pour the dressing over the quinoa and vegetables and toss to coat. Cover and refrigerate for several hours. Remove from refrigerator 15 minutes before serving. Taste and add salt and pepper as needed.