Warm the pot. Set a large soup pot over medium heat and add the olive oil. When it shimmers, add onion, carrot, and celery with a pinch of salt. Cook 6–8 minutes, stirring now and then, until the vegetables soften and the edges look glossy.

Add garlic and tomato paste. Stir in the garlic and cook 30 seconds until fragrant. Add the tomato paste and cook 1–2 minutes to deepen the flavor and take off its raw edge.

Build the base. Add crushed tomatoes, lentils, broth, bay leaf, thyme, cumin, paprika, and the diced potato if using. Stir well, scraping up any browned bits from the bottom of the pot.

Simmer gently. Bring to a boil, then reduce to a simmer. Cover partially and cook 25–35 minutes, stirring occasionally, until lentils are tender but not mushy. If the soup thickens too much, add a splash of water or broth.

Add greens. Stir in kale or spinach and cook 2–4 minutes, until wilted and tender. Turn off the heat.

Brighten and season. Remove the bay leaf. Add lemon juice (start with half a lemon, then adjust). Taste and season generously with salt and black pepper. If you like, add a little lemon zest for extra brightness.

Finish and serve. Ladle into bowls and top with chopped parsley. Serve with crusty bread, a dollop of yogurt, or a drizzle of olive oil if you want a richer finish.