Sauté the aromatics: In a medium saucepan, warm the olive oil over medium heat.
Add the sliced leek and diced bell peppers.
Cover and cook for 5 minutes, until tender.
Toast the quinoa: Stir in the rinsed quinoa and minced garlic.
Cook, uncovered, for 3-4 minutes, stirring frequently, until the quinoa is lightly toasted and fragrant.
Cook the quinoa: Pour in 3 cups (720 ml) of water and season with salt.
Bring to a boil, then reduce heat to a simmer, cover, and cook for 15 minutes, or until the water is absorbed.
Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.
Prepare for baking: Preheat your oven to 350°F (175°C).
Coat a 13x9-inch baking dish with cooking spray.
Mix the casserole: In a large bowl, whisk the eggs and milk.
Fold in the cooked quinoa mixture and 1½ cups of grated Cheddar cheese until everything is evenly combined.
Bake to perfection: Transfer the mixture to the prepared baking dish.
Sprinkle with additional cheese, if using.
Bake for 30-35 minutes, until the edges are browned and the center is set.
Let it rest for a few minutes before serving.
Don't skip rinsing the quinoa! This crucial step removes its natural coating, called saponin, which can cause a bitter or soapy taste.
