In a large pot or Dutch oven, heat the olive oil over medium heat.

Add the diced onion, carrots, and celery. Sauté for about 5–7 minutes until softened and translucent.

Stir in the minced garlic, oregano, thyme, and red pepper flakes (if using). Cook for another 1–2 minutes until fragrant.

Add the rinsed lentils, diced tomatoes (with their juices), and vegetable broth to the pot. Stir gently to combine.

Increase the heat to bring the mixture to a boil, then reduce the heat to low and cover.

Let the soup simmer for about 30–35 minutes, or until the lentils are tender.

Once the lentils are tender, stir in the chopped spinach (or kale) and cook for an additional 5 minutes.

Taste and adjust seasoning with salt and pepper. Add lemon juice if desired.

Ladle the soup into bowls and garnish with fresh parsley. Serve hot.