Place the red lentils in a strainer or colander. Rinse with water and remove any lentil stones. Set aside.
In a small bowl, combine the salt, cumin, cayenne pepper, black pepper, and chili powder. Set aside.
In a large soup pot over medium-high heat, heat the olive oil. Place the onion, celery, and garlic in the pot and sauté until tender, about 8 minutes. Add the spices and continue to cook for about another minute, until fragrant.
Add the tomatoes, Tabasco, water, vegetable stock, and lentils to the pot and simmer 20-25 minutes, until lentils are tender. When the lentils are done, combine the cornstarch and cold water in a small bowl and stir until dissolved. Slowly add to the soup and stir until evenly dispersed. Remove from heat and serve immediately. Leftovers can be kept in an airtight container in the refrigerator up to 5 days. Soup freezes well, up to 3 months. Thaw overnight in refrigerator before serving.