In a food processor combine bread, lemon zest, walnuts and cheese. Pulse until almost uniform in texture. Continue pulsing while drizzling in the olive oil. Set aside.
Season fish with salt and pepper. Place 4 fillets in a single layer on a buttered 9 by 12-inch casserole. In a small saucepan melt 4 tablespoons of butter and add the lemon juice and capers. Pour butter mixture over fish, and sprinkle tops with bread crumb mixture. Bake uncovered for 15 to 20 minutes.
Meanwhile, add the olive oil to a large skillet over medium heat. Infuse the oil with minced garlic, then add the Swiss chard and saute until wilted, about 2 minutes. Season with salt and pepper, to taste. Serve hot with the sole.