Mix the cucumber and water together in a pitcher and refrigerate to infuse until serving.

Heat a pot over medium heat. Once hot, add the olive oil. Sauté the onion, carrot, celery, and garlic until they start to soften.

Stir in the chicken broth, diced tomato, thyme, and lentils. Bring to a simmer and cook for about 20 to 30 minutes, until the lentils are soft and the soup builds flavor.

Check the lentils for doneness—they should be tender but not mushy. Remove the thyme sprigs before serving.

Ladle the soup into bowls and serve with cheese and crackers, and cucumber water.