Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium heat.
Add the onion, carrots, and celery. Cook for 5-7 minutes until vegetables begin to soften.
Stir in the minced garlic, oregano, cumin, and bay leaf. Cook for 1 minute until fragrant.
Add the rinsed lentils and diced tomatoes with their juices, stirring to combine with the vegetables.
Pour in the broth and bring the mixture to a boil.
Reduce heat to low, cover, and simmer for 35-40 minutes, until the lentils are tender but not mushy.
Add the chopped greens and cook for an additional 5 minutes until wilted.
Remove from heat and stir in the fresh lemon juice.
Season with salt and pepper to taste.
Remove the bay leaf before serving.
Ladle into bowls and garnish with freshly chopped parsley.