Heat the oil in a large pot over medium heat. Add the onion, carrots and celery with a pinch of salt and cook, stirring occasionally, for 8–10 minutes until softened.
Stir in the garlic, cumin and paprika and cook for 1 minute until fragrant.
Add the lentils, tomatoes, broth and bay leaf. Bring to a boil, then lower to a gentle simmer and cook, partly covered, for 25–35 minutes, until the lentils are tender.
Remove the bay leaf. Stir in the kale and simmer 3–5 minutes more until wilted.
Finish with the lemon juice, then season with salt and pepper. Add more broth if you like it thinner.