Prepare the Stuffing
Heat a small pan with olive oil over medium-low heat.Sauté pancetta until lightly rendered. Add garlic and cook just until fragrant.Transfer to a bowl and mix with breadcrumbs, parsley, herbs, Pecorino, black pepper, and optional fennel seeds.Stir in the beaten egg until the mixture is moist and just holds together.Stuff the Pork
Lay the butterflied pork loin flat and season lightly with salt and pepper.Spread stuffing evenly over the meat, leaving a small border.Roll tightly and tie securely with kitchen twine every 1½–2 inches.Prepare the Vegetables
Toss fennel, potatoes, carrots, and garlic with olive oil, salt, and pepper.Spread evenly in a large roasting pan.Roast
Preheat oven to 375°F (190°C).Place the stuffed pork loin on top of the vegetables.Pour white wine or broth around the vegetables (not over the pork).Roast uncovered for about 25 minutes per pound, until the internal temperature reaches 140–145°F.Rest & Serve
Remove from oven and rest the pork for 15 minutes before slicing.Slice thick and serve with roasted vegetables and pan juices spooned over the top.