Heat the olive oil in a large pot over medium heat. Add the diced onion, carrots, and celery. Sauté for 5-7 minutes, or until the vegetables begin to soften and the onion becomes translucent. Stir occasionally to prevent sticking.

Stir in the minced garlic, dried oregano, dried basil, and red pepper flakes (if using). Cook for another minute until fragrant. Be careful not to burn the garlic, as it can become bitter.

Add the rinsed lentils, vegetable or chicken broth, diced tomatoes (undrained), and bay leaf to the pot. Stir well to combine all ingredients.

Bring the soup to a boil, then reduce heat to low, cover, and simmer for 30-40 minutes, or until the lentils are tender and the soup has thickened slightly. Stir occasionally during simmering to prevent lentils from sticking to the bottom of the pot.

Remove the bay leaf. Season the soup with salt and freshly ground black pepper to taste. Start with about 1 teaspoon of salt and 1/2 teaspoon of pepper, and adjust as needed. Ladle into bowls, garnish with fresh parsley and grated Parmesan cheese (if desired). Serve hot and enjoy every comforting spoonful!