For potatoes: Bring potatoes to a boil in well salted water. Render some of the fat from the andouille, add shallot, and cook until softened. When potatoes are tender, drain well and combine with andouille shallot mixture. Adjust seasoning and mix in chopped parsley and dill. Reserve.
For the nage: Heat oil in a sauce pot. When very hot, quickly sauté mushrooms, add shallot and garlic. Deglaze with the white wine, add fish stock, and slowly reduce by 1/4. When ready to plate, incorporate 2T of butter.
For the pesto: Combine greens, lemon, and chili in a food processor and pulse a few times. With machine running, slowly incorporate olive oil. Season.
Lightly season filets with berbere, salt, black pepper, and olive oil. In a hot sauté pan, place fish skin-side down, lightly press to ensure skin stays in contact with the pan. Cook for 2-3 minutes, flip and finish for 1-2 minutes more (depending on the thickness of the filet).