Part 1: Preparing the Bell Peppers

1. Preheat and Prep: Preheat your oven to 400°F (200°C). Line a 9×13 inch baking dish or a large baking sheet with parchment paper for easy cleanup.
2. Cut the Peppers: Wash and dry the bell peppers. Slice each pepper in half lengthwise, from the stem down to the base. Use a small knife to carefully remove the seeds and the white membranes from each half. The goal is to create 12 boat-like pepper halves.
3. Pre-Bake the Peppers: Arrange the pepper halves, cut-side up, in the prepared baking dish. Drizzle them with 1 tablespoon of olive oil and sprinkle with 1/4 teaspoon of salt and a pinch of black pepper. Rub the oil and seasonings over the inside and outside of each pepper half. Bake them for 15-20 minutes. This crucial step softens the peppers and removes some of their moisture, preventing a watery final dish and ensuring the peppers are tender and sweet.

Part 2: Creating the Savory Filling

1. Sauté the Aromatics: While the peppers are pre-baking, heat 1 tablespoon of olive oil in a large skillet or pan over medium heat. Add the finely chopped onion and sauté for 5-7 minutes, until it becomes soft and translucent. Add the minced garlic and red pepper flakes (if using) and cook for another minute until fragrant. Be careful not to burn the garlic.
2. Add the Spinach: Add the thawed and thoroughly squeezed spinach to the skillet. Use a wooden spoon to break it up and mix it with the onions and garlic. Cook for 2-3 minutes to heat it through and evaporate any remaining moisture.
3. Combine the Filling Ingredients: Remove the skillet from the heat. Add the 2 cups of cooked quinoa, the crumbled feta cheese, the optional grated Parmesan, the dried oregano, and the lemon zest to the skillet.
4. Season and Mix: Stir everything together until well combined. The feta will soften slightly from the residual heat. Taste the mixture and season generously with salt and freshly ground black pepper. Remember that the feta is already salty, so taste before adding too much salt.

Part 3: Stuffing and Baking to Perfection

1. Stuff the Peppers: Carefully remove the pre-baked peppers from the oven. Using a spoon, generously fill each pepper half with the spinach and feta mixture. Mound the filling on top—don’t be shy!
2. Final Bake: Place the stuffed peppers back into the oven. Bake for an additional 20-25 minutes, or until the filling is heated through and the tops are lightly golden brown. If you like a crispier top, you can switch the oven to broil for the last 1-2 minutes, but watch them very closely to prevent burning.
3. Rest and Garnish: Remove the peppers from the oven and let them rest in the baking dish for at least 5-10 minutes. This allows the filling to set and makes them easier to serve. Just before serving, sprinkle with freshly chopped parsley for a burst of color and freshness.