As this layered slow-cooker squash casserole recipe cooks, the liquid from the tangy tomatillo salsa and summer squash is absorbed by the quinoa, adding tons of flavor to the final dish.
Combine tomatillos, tomatoes, pepper, onion, lime juice and salt in a medium bowl.
Coat a 5- to 6-quart slow cooker with cooking spray. Layer quinoa, 1/3 cup cheese and all of the squash in the slow cooker. Top with another 1/3 cup cheese. Spread the tomatillo mixture on top; but don't stir the ingredients together. (Refrigerate the remaining cheese to use for the topping.)
Cover and cook on Low for 4 hours. Serve sprinkled with oregano and the remaining 1/3 cup cheese.