For the topping:
Sauté the bacon until crisp. Place on paper towels to drain and reserve. Discard the rendered bacon fat or save for another use.
Trim the stem of each sprout down to the first ring of petals. Break off the petals. Continue to do this until you reach the tight bud of the sprout. Reserve the bud for another use and place the petals into a measuring cup.
Place 2 c. of water into a small sauce pan. Bring the water to boil. Add the salt. Add the Brussels sprout petals to the boiling water and blanch for 30 seconds. Strain the petals from the water and immediately rinse in cold water. Dry the petals on paper towel and reserve.
For the fish:
Preheat the oven to 450°F/230°C.
Lay the fish portions out on a clean work surface and sprinkle lightly with sea salt.
Preheat a 5-qt. nonstick sauté pan on medium-high heat until the rim of the pan is hot to the touch. Add 1 Tbsp. olive oil and allow to heat for an additional minute. Swirl the oil in the pan.
Place the fish into the pan skin side down. Sauté the fish on the range top until it begins to turn opaque (approximately 3 minutes).
When the fish has turned opaque 1/4-in. up the side, place the pan with the fish into the preheated oven. Bake the fish for and additional 3 - 4 minutes to finish cooking. (For fish, allow 7 minutes of cooking time for each inch of thickness.)
Remove the fish from the oven and leave in the pan.
While the fish is in the oven, preheat a 10-in. nonstick omelette or fry pan on medium-high heat. When the rim of the pan is hot to the touch add the 2 Tbsp. olive oil. Allow the oil to heat for a minute.
Add the mushrooms and sauté until crisp and carmelized. Add the Brussels sprouts petals and sauté for an additional minute or two. Finally add the bacon pieces to the pan and sauté for an additional minute. Add a few small splashes of balsamic vinegar.
Transfer the fish to warm plates and top with mushroom mixture. Serve.