Pork Tenderloin Scallopine with Lentil-Vegetable Salad

To make the salad:

1 1/2 cups lentilles de Puy (or use regular lentils)
4 tablespoons butter, divided use
salt and freshly ground black pepper to taste
3 small carrots, or 1 large, diced
1 small zucchini, diced
1 medium onion, diced
2 ribs celery, diced
2 tablespoons extra virgin olive oil
2 tablespoons balsamic vinegar

To make the pork scallopine:

1 pork tenderloin, cut into 3/4-inch medallions
salt and freshly ground black pepper to taste
about 3/4 cup Dijon mustard
1 cup flour (or use gluten-free flour)
extra-virgin olive oil for frying