In a medium saucepan, bring 3 cups water to a boil over high heat. 

Stir in lentils, lower heat and simmer until lentils are just tender, 18 to 20 minutes. 

Drain and set aside.

Meanwhile, place arctic char, 4 tablespoons of the vinegar and 1/4 cup of the shallots in the pan used for cooking lentils (fold tail under fillet if necessary so it fits in the pan). 

Add enough water to just cover fish. 

Bring to a simmer, lower heat, cover and cook until fish is just opaque in the center, 5 to 6 minutes. 

Remove fish with a slotted spoon and transfer to a plate, leaving on any shallots that cling to the fish.

Place pear in the same pan, set over medium heat and cook until just warm, about 1 minute. 

Add remaining 1/4 cup shallots and cooked lentils, cover and cook, stirring occasionally, until warmed through, 4 to 5 minutes. 

In a small bowl, whisk together mustard, pepper, salt and remaining 3 tablespoons vinegar. 

Pour over lentils, add green onions and parsley and toss to combine. 

Flake fish away from skin and serve over lentils.