01 - Set oven to 425°F (220°C) to prepare for roasting peppers.
02 - Halve red bell peppers, remove seeds and membranes, then place cut side down on a baking sheet lined with parchment paper.
03 - Roast peppers for 20 to 25 minutes until skins blister and char. Transfer to a bowl, cover with plastic wrap, and let steam for 10 minutes before peeling skins and chopping flesh.
04 - In a large pot, heat olive oil over medium heat. Add chopped onion, carrot, and celery; cook for 5 to 7 minutes until softened.
05 - Incorporate minced garlic, smoked paprika, cumin, and optional chili flakes; sauté for 1 minute until fragrant.
06 - Add chopped roasted peppers and rinsed lentils to the pot. Pour in vegetable broth.
07 - Bring mixture to a boil, then reduce heat and simmer uncovered for 20 to 25 minutes until lentils are tender.
08 - Use an immersion blender or transfer portions to a blender to purée soup until desired consistency is achieved; leave slightly chunky if preferred.
09 - Adjust seasoning with salt and black pepper.
10 - Ladle soup into bowls, garnish with fresh parsley and a squeeze of lemon juice.