Combine the quinoa with 1 cup water in a small saucepan. Bring to a slow boil, then lower the heat, cover, and simmer until the water is absorbed, about 15 minutes.
Meanwhile, heat the oil, broth, or water in a medium skillet. Add the onion and sauté until translucent. Add the bell pepper and sauté until both are golden.
Add the remaining ingredients except the bread of choice, and bring to a gentle simmer. Cook over medium-low heat, loosely covered, for 5 to 7 minutes, stirring occasionally. Let the skillet stand off the heat for 5 minutes to allow the flavors to mingle further and for the quinoa to absorb the tomato flavors.
Evenly spoon the filling over the bottoms of whole-grain rolls, cover with the tops, or serve open-faced.