Preheat your oven to 375°F. While it heats, prepare the bell peppers by carefully cutting off the top quarter of each pepper around the stem, then use a small knife or spoon to remove the seeds and white membrane from inside, creating a hollow cavity for filling. Stand the prepared peppers upright in a lightly oiled baking dish, arranging them snugly so they support each other and won't tip over during baking.

Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced onion and cook for 3-4 minutes, stirring occasionally, until it becomes translucent and softens. Add the minced garlic and cook for another minute until fragrant, being careful not to let it brown. This aromatic foundation builds the flavor base for your filling.

Add the spinach to the skillet in batches, stirring and allowing each addition to wilt before adding more—this usually takes 3-4 minutes total. Once the spinach is fully wilted and any excess moisture has evaporated slightly, drain the fire-roasted tomatoes to remove excess liquid, then add them to the pan and stir well to combine. Remove from heat and let cool slightly while you prepare the grain mixture.

In a large mixing bowl, combine the rinsed quinoa, cooked lentils, finely chopped fresh dill, fresh parsley, oregano, salt, and black pepper. Mix well to distribute the herbs and seasonings evenly throughout. This dry mixture serves as the foundation that holds your filling together and ensures every pepper bite has a balanced flavor of herbs and grains.

Add the cooled vegetable mixture from Step 3 to the grain mixture in the bowl and stir well to combine. Pour in the lemon juice and fold in the crumbled feta cheese gently, being careful not to over-mix so the feta maintains some texture. Taste and adjust seasoning with salt and pepper as needed—I like to add an extra squeeze of lemon juice if the filling needs brightness. The filling should be moist but not wet, with a balanced Mediterranean flavor.

Spoon the filling evenly into each prepared pepper, packing it gently and mounding slightly at the top. Fill all 10 peppers, then cover the baking dish tightly with foil to trap steam and help the peppers cook through. Bake for 30 minutes, until the peppers are tender when pierced with a fork but still hold their shape.

Remove the peppers from the oven and carefully take off the foil to release the steam. Let the peppers rest in the dish for 5-10 minutes before serving—this helps them set and makes them easier to plate without falling apart. Serve warm or at room temperature, as these stuffed peppers are delicious both ways.