Heat the oven. Preheat to 400°F (200°C). Lightly oil a baking dish large enough to hold all the peppers upright. If using tomato sauce, spread it in a thin layer on the bottom of the dish.

Prep the peppers. Slice off the tops, then remove seeds and membranes. If they wobble, trim a sliver off the bottoms to help them stand. Brush or rub the shells with a bit of olive oil and a pinch of salt.

Soften the aromatics. In a large skillet over medium heat, warm 1–2 tablespoons olive oil. Add the chopped onion and a pinch of salt. Cook 3–4 minutes until translucent. Stir in garlic and cook 30 seconds until fragrant.

Wilt the spinach. Add the spinach to the pan in batches. Toss until just wilted, 2–3 minutes. Remove from heat and let it cool slightly. Squeeze out any excess moisture, then chop.

Build the filling. In a bowl, combine chopped spinach, cooked rice or quinoa, crumbled feta, ricotta or cottage cheese, lemon zest, a squeeze of lemon juice, dried oregano, red pepper flakes (if using), and fresh parsley or dill. Season with salt and pepper. Taste and adjust. The filling should be well-seasoned and bright.

Fill the peppers. Spoon the mixture into the pepper shells, packing lightly to avoid air pockets. Leave a little space at the top. Sprinkle with a touch of Parmesan if you like.

Bake. Arrange peppers upright in the baking dish. Add a splash of water (2–3 tablespoons) around them if you’re not using tomato sauce. Cover loosely with foil and bake 25 minutes. Remove foil and bake another 10–15 minutes, until the peppers are tender and the tops lightly golden.

Finish and serve. Let the peppers rest 5–10 minutes. Squeeze a little more lemon over the top, drizzle with olive oil, and add extra herbs. Serve warm with a simple salad or crusty bread.