1 1/2cupsfreshly grated reduced fat cheesedivided (I used half mozzarella, half extra sharp cheddar), about 6 ounces
Bring 2 cups chicken broth to a boil in a saucepan, then add the quinoa. Reduce heat to a simmer, cover, and let cook until the liquid has been mostly absorbed and the quinoa is tender, about 15 minutes, depending upon the brand of quinoa you purchase. Keeping the pan covered, remove from heat and let stand 10 minutes. Uncover, lightly fluff with a fork, and set aside.
Preheat oven to 350 degrees. Spray an 8x8-inch baking dish or other 2-quart casserole dish with nonstick spray then set aside.
Heat 1 tablespoon olive oil in a large, deep skillet or Dutch oven over medium high. Add the chicken, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Cook the chicken just until no longer pink on the outside (it does not need to be completely cooked through), about 3 minutes. With a slotted spoon, remove the chicken to a plate and set aside.
Reduce the skillet heat to medium. Add the remaining 2 teaspoons olive oil, diced bell pepper, corn, zucchini, garlic, and half of the green onions. Cook until frangrant and the corn is softened, about 5 minutes. Remove to the plate with the chicken.
Melt the butter in the skillet, then sprinkle the flour over the top and briskly whisk to coat the flour with butter and break it up. Let cook until the flour is golden and smells lightly nutty, about 30 seconds to 1 minute, Slowly pour in the remaining 1 cup chicken broth, then the milk, adding a few splashes of liquid at a time. Whisk constantly and pause as needed to break up any lumps. Add the oregano and remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper. Increase the heat to bring the mixture to a simmer, then reduce the heat and let gently bubble until the sauce has thickened slightly, about 5 minutes, stirring often.
Remove skillet from heat, then stir in the cooked quinoa, chicken, reserved veggies, and half of the cheese. The mixture will be liquidy. Carefully pour into the prepared baking dish and sprinkle the remaining cheese and green onions on top.
Place the mixture on top of a rimmed baking sheet (this will catch any spill over). Bake for 20-25 minutes, until the top is golden and bubbly. Let cool 10 minutes, then serve.
This Cheesy Quinoa Casserole can be frozen baked or unbaked. Let thaw in the refrigerator overnight prior to baking or reheating.
Store leftovers in an airtight container in the refrigerator for up to 4 days.