Preheat your oven to 375 degrees Fahrenheit and lightly grease a 9x9 inch baking dish.
Heat the olive oil in a skillet over medium heat, add the diced onions, and cook for 5 minutes until soft.
Stir in the minced garlic, oregano, and cumin. Cook for 1 minute until fragrant.
Add the fresh spinach to the skillet in handfuls, tossing until completely wilted.
Combine the rinsed quinoa, drained lentils, wilted spinach mixture, vegetable broth, salt, and pepper in a large mixing bowl. Stir well.
Pour the mixture into the prepared baking dish, cover tightly with foil, and bake for 35 minutes.
Remove the foil and bake for an additional 10 to 15 minutes until the liquid is absorbed. Let rest for 10 minutes before serving.