Combine lentils, chicken stock, diced onion, carrot pieces, and celery pieces in a pot.

Simmer for 35 minutes or until lentils are tender.

Remove and discard celery. Cut the carrot into smaller pieces and return to the lentils.

Set lentil mixture aside.

In a separate pan, sauté pancetta until crisp. Drain and set aside.

Drain the pancetta drippings, adding butter if necessary, and sauté the mushrooms.

Add minced garlic to the mushrooms and continue to sauté.

Once the mushroom mixture is golden brown, add rosemary, thyme, balsamic vinegar, mustard, and olive oil.

Gently fold in the cooked lentils and reserved pancetta.

Season to taste with salt and pepper.