Preheat the grill by lighting a full chimney of charcoal and position for direct grilling. Prepare the fish by scoring filets on both sides of the fish, then skewer the trout through the mouth and out the tail. Brush inside and out with olive oil, then season liberally with salt, pepper and garlic. Fill each cavity with a tablespoon of pesto, add shallot, lemon and fresh herbs. Grill the fish over medium-high direct heat for 3-4 minutes per side. Remove from heat and tent for at least 5 minutes prior to serving. Garnish with thyme leaves and lemon zest. Splash with olive oil, season additionally, to taste, and serve.