In a large pot, heat the olive oil over medium heat. Add the chopped onion and garlic. Sauté for 3-4 minutes until the onion becomes translucent.
Add the diced carrots, celery, and red bell pepper to the pot. Cook for an additional 5 minutes, stirring occasionally.
Stir in the diced tomatoes along with their juices, zucchini, and rinsed lentils. Cook for 2-3 minutes, allowing the flavors to combine.
Pour in the vegetable broth and add the ground cumin, smoked paprika, dried thyme, salt, and pepper. Bring to a boil, then reduce the heat to a simmer.
Let the soup simmer for 25-30 minutes, or until the lentils and vegetables are tender.
A few minutes before serving, stir in the chopped kale or spinach and allow it to wilt. Adjust seasoning if necessary.
Remove the soup from heat and stir in the lemon juice for a fresh finish.
Ladle the soup into bowls and garnish with fresh parsley.
Notes
Adjust seasoning to taste and add more vegetables if desired.