Rinse 1 cup red lentils under cold water until the water runs clear; set aside.
Heat 2 tbsp olive oil in a large pot over medium heat.
Add chopped onion and sauté 5–7 minutes until soft and translucent.
Stir in diced carrots and bell pepper; cook 4–5 minutes until slightly softened.
Add minced garlic and spices (cumin, coriander, paprika, turmeric); cook 1 minute until fragrant.
Pour in 1 cup crushed tomatoes and 4 cups vegetable stock; stir to combine.
Add the rinsed lentils, bring to a gentle boil, then reduce heat to a simmer.
Simmer uncovered 20 minutes, stirring occasionally, until lentils are tender and begin to break down.
Use an immersion blender to purée until smooth, or leave partially chunky if preferred.
Season with salt, pepper and lemon juice; adjust consistency with extra stock or water if too thick. Serve hot with a drizzle of olive oil or a spoonful of yogurt and a sprinkle of chopped herbs.