Rinse trout under cold water and pat dry. Remove any remaining bones with tweezers. Generously season with salt and pepper.
Heat 2 teaspoons of the Roasted Garlic Oil in a medium skillet. Add onion and sauté over medium heat until soft and lightly colored, 3-4 minutes. Add spinach, Roasted Garlic Onion Jam and 2 Tablespoons of water. Bring mixture to a boil and stir to dissolve the jam. Continue cooking until liquid evaporates, about 1 minute.
Stir in pine nuts, plenty of black pepper and cayenne pepper, if desired. Set aside to cool.
Turn on broiler. Position oven rack about 5-6 inches from heat. Place a piece of lightly oiled aluminum foil on a cookie sheet.
Fill trout with spinach mixture, packing it well, and place on a cookie sheet. Broil for 4 minutes on each side. Turn off broiler and let trout rest in oven for 4 minutes longer.
Whisk together yogurt, the remaining 2 Tablespoons of Roasted Garlic Oil, scallions and salt and pepper to taste. Remove top skin from trout and transfer to plates. Ladle some yogurt sauce over trout and pass remaining sauce at table.