Rinse the red lentils thoroughly until water runs clear, then set aside.
Heat olive oil in a large pot over medium heat. Add onions and sauté until translucent, about 5 minutes.
Add minced garlic and grated ginger, cook for another minute until fragrant.
Stir in tomato paste and all the spices (paprika, cumin, turmeric, cinnamon, and cardamom). Toast the spices for 30 seconds until aromatic.
Add the rinsed red lentils and vegetable broth. Bring to a boil, then reduce heat and simmer, partially covered, for 20-25 minutes until lentils are tender and the stew has thickened.
Stir occasionally to prevent sticking. Add more broth if needed.
Once lentils are cooked, stir in lemon juice and season with salt and pepper to taste.