Heat oven to 350°F with rack set in middle position. Coat a 3-quart or 9×13-inch baking dish with nonstick spray or butter; set aside.

Arrange bread in an even layer on a baking sheet. Bake bread in oven until toasted and starting to brown, 20–25 minutes. 

Meanwhile, cook pork in a sauté pan over medium heat until cooked through, about 4 minutes. Stir in fennel seeds, pepper flakes, and nutmeg, cook 1 minute. Season with salt and black pepper and transfer to a large bowl.

Heat butter and/or oil in now-empty sauté pan over medium-high heat. Add mushrooms and shallots and cook until liquid is evaporated and mushrooms are browned 10–12 minutes.

Stir in celery and cook 2 minutes. Stir in chard, sage, and garlic and cook 30 seconds. Deglaze pan with 2 tablespoons lemon juice then transfer to bowl with pork; season with salt and pepper.

Add bread, parsley, and 1 teaspoon lemon zest to bowl with mushrooms and pork and toss to combine.

Whisk together broth and eggs then pour over bread mixture and toss until thoroughly combined.

Transfer dressing to prepared baking dish and cover tightly with a piece of foil lightly sprayed with nonstick spray. Bake dressing, covered, 20 minutes. Remove foil from dish and continue baking dressing until top is golden brown and edges are crisp, 30–40 minutes.

Let dressing cool 5 minutes, sprinkle with additional chopped parsley and serve.