Preheat the grill or broiler.
In a small saute pan, heat the olive oil over medium-low heat, then add the rosemary and garlic. Cook until softened, about 5 minutes. Add the olives and cook another 3 minutes.
Lay each trout out on 6 sheets of aluminum foil and season with salt and pepper. Drizzle some of the olive mixture over each fillet. Wrap each fillet with 2 slices of pancetta, securing with a toothpick.
Wrap fillets in the foil and grill or broil for 10 minutes, until fish is cooked through. Serve immediately.