Finely dice carrots, onion, celery, and leeks into bite-sized pieces (similar in size to lentils for even cooking). Rinse green lentils under cold water and set aside.
Heat 2 tablespoons of olive oil in a large soup pot over medium heat. Add chopped onions, carrots, celery, and leeks. Sauté for 5–6 minutes, stirring occasionally, until vegetables are tender and onions are translucent.
Add minced garlic, dried thyme, and curry paste to the pot. Sauté for 3–4 minutes until the spices are fragrant.
Stir in tomato paste and cook for 2 minutes, stirring constantly, to caramelize and deepen the flavor.
Add rinsed lentils, vegetable stock, bay leaf, salt, and black pepper to the pot. Stir well, then bring to a boil.
Reduce heat to a simmer and cook for 25–30 minutes, or until lentils are tender but not mushy.
Remove the bay leaf. Taste and adjust seasoning as needed. Serve hot.