Sweat onions and carrots in a pot with one tbsp oil, 2 oz water, and 1/2 tsp of salt. When onions are clarified, add lentils, broth, garlic, tomato paste, cumin and cayenne. Bring to a boil over med-high heat. Lower heat and simmer, uncovered, until vegetables are very tender and lentils begin to fall apart, about 20 minutes. Squeeze in lemon and stir before serving