In a large pot, sautee onions, carrots, celery, and 1 tsp of salt in hot oil for about 8-10 minutes, allowing everything to caramelize and turn brown.
Add the garlic, cook for another 30 seconds, and then stir in the tomato paste. Cook for about 1 minute, using your spoon to loosen up the brown bits on the bottom of your pan.
Add 4 cups of water and 4 cups of stock, along with the lentils, thyme, bay leaf, oregano, red pepper flakes, lemon zest, 2 tsp salt, and 1 tsp of black pepper. Bring to a boil and then reduce heat to low.
Simmer with the lid on for 25-30 minutes, until the lentils are soft but not mushy.
Remove the bay leaf and separate 2 ½ cups of the soup. Puree the separated soup and then add it back to the pot.
Stir in the lemon juice and parsley, and then serve warm.