Rinse 1 cup lentils under cold water
Heat 1 tablespoon oil in a pot over medium heat
Add 1 chopped onion and cook until soft
Add 2 minced garlic cloves and cook for 1 minute
Add 1 chopped carrot and 1 chopped celery stalk
Stir in 1 teaspoon salt, 1/2 teaspoon black pepper, and 1 teaspoon cumin
Add 1 cup lentils and 4 cups water or broth
Bring to a boil
Reduce heat and simmer for 25 to 35 minutes
Stir occasionally until lentils are tender
Add more water if needed
Taste and adjust seasoning
Serve hot