Blend chopped onion chopped red bell pepper, chopped tomatoes, garlic cloves, olive oil, and chopped leek to make the base for the soup. Place a pan on a low flame and pour the soup base. Mix with tomato puree. Season with salt and cracked black pepper. Pour some vegetable stock. Cook on low flame for 10 minutes. Keep stirring. Add some red chilli flakes and basil leaves. Once cooked, blend again. Transfer the soup to a serving bowl. Garnish with some chilli oil and basil leaves.