Heat the 2 tablespoons olive oil in a medium saucepan.
Add the garlic, celery, and carrot and cook over medium heat until fragrant, about 6 minutes.
Add the lentils, 1/2 teaspoon sea salt, and just enough water to cover. Bring to a boil, reduce the heat to low, and simmer until just soft, 30 to 35 minutes.
Drain the lentils.
Meanwhile, pulse together the mustard, vinegar, and herbs in a food processor or blender, or whisk together by hand.
Drizzle in the remaining 1/4 cup (60 ml) olive oil and pulse or whisk to bring together.
Add 1/4 teaspoon sea salt and season with pepper. Taste and add more salt as needed.
Spoon the warm lentils onto plates. Top with the mozzarella and sprinkle the mozzarella with coarse sea salt. Top the lentils and mozzarella with the pine nuts and drizzle with the herb vinaigrette.