Rinse lentils with hot water for 1-2 minutes until water runs clear. Peel potato and onion; cut both into small cubes.
Bring 5 glasses water to boil in large saucepan over medium-high heat.
Add lentils, potato cubes, onion cubes, and 1 teaspoon of salt. Cook over medium-high heat until potatoes are tender, about 15 minutes.
Reduce heat to low. Stir in chicken broth cube (or vegetable broth) and 1 teaspoon of mint. Season with paprika powder and salt to taste.
Simmer on low heat for 2 minutes to let flavors infuse.
While soup simmers, melt 2 tablespoons margarine in small saucepan over medium heat. Add 2 tablespoons tomato paste and a pinch of salt; stir until well combined.
Remove lentil pot from heat. Carefully puree soup until smooth using an immersion blender or regular blender.
Place pot back on stove over medium heat. Stir in tomato paste mixture. Increase heat to medium-high and bring to boil, stirring occasionally, about 2-3 minutes.
Serve hot with flatbread and lemon. For extra spice, serve with chili peppers or pul biber (Turkish red pepper flakes) on the side.