Heat the oven to 350 degrees F (175 degrees C).

Melt 4 tablespoons of butter in a small pot.

Stir in the breadcrumbs, half the minced shallots, chopped parsley, and lemon zest.

Season the breadcrumb mixture with kosher salt and freshly ground pepper.

Sprinkle both sides of the halibut fillets with kosher salt and freshly ground pepper.

Spread a thin layer of mayonnaise on top of each halibut fillet.

Press the panko mixture on top of the mayonnaise layer on each fillet.

Heat the remaining 3 tablespoons of butter in a 12-inch skillet over medium heat.

Add the sliced rainbow chard stems and remaining minced shallots to the skillet.

Cook the chard stems and shallots for about 2 minutes, until slightly softened.

Turn off the heat.

Fold in the torn chard leaves, 2 tablespoons of water, kosher salt, and freshly ground pepper to taste.

Place the halibut fillets on top of the chard leaves in the skillet.

Transfer the skillet to the preheated oven.

Bake until the fish is just cooked through, about 15 to 20 minutes.