1. Preheat the oven to 200°C (400°F). Put the bell pepper and onion in a bowl. Add olive oil, salt, pepper, mix, then place them on a baking sheet lined with parchment paper. Bake for 15 minutes. Let the bell pepper cool, remove the skin, and cut it into strips.
2. Meanwhile, cook the lentils according to the package instructions. Toast the nuts in a dry skillet.
3. Mix all the ingredients for the vinaigrette together, with salt and pepper.
4. In a salad bowl, combine the lentils, spinach, arugula, red peppers, onions, add the olives, parsley, nuts, feta cheese, and drizzle with vinaigrette.