Heat 2 tablespoons oil in a deep sauté pan over high heat.

Add shallots and cook until soft, about 5 minutes. Add garlic and carrots and sauté until just beginning to brown, about 10 minutes.

Add lentils, mix until just heated through, season to taste with salt and pepper. Remove to a bowl, cover, and set aside.

Wipe out the pan. Pat dry salmon fillets with paper towels. Season with salt and pepper. Heat remaining 1 tablespoon oil in the sauté pan over high heat.

Once hot, add salmon, skin side down. Cook until fish lifts easily, about 5 minutes.

Flip salmon and cook 1 to 2 minutes more for medium or to desired doneness.

Prepare sauce: Whisk together sour cream, mustard, and lemon zest and juice.

Serve lentils with salmon on top and sauce on the side.