Place the lentils, water, and broth base in a pot. Cover and bring to a boil over medium-high heat. Reduce the heat to medium and cook for 15 to 20 minutes, until the lentils are tender but firm.
Remove from the heat, drain any remaining liquid, and transfer the lentils to a large bowl. Chill for at least 30 minutes.
Stir in the celery, tomatoes, shallots, and parsley.
In a small dish, make the dressing by whisking together the olive oil, mustard, vinegar, herbes de Provence, black pepper, and garlic.
Add the dressing to the lentil mixture and toss. Taste and season with sea salt, if desired. Chill until serving time.