Drizzle 2 sheets of foil with olive oil; sprinkle each with 1/4 cup sliced almonds and 3/4 teaspoon crushed coriander seeds. Brush four 6-ounce trout fillets with more olive oil; season with salt and pepper. Place each fillet, skin-side down, on top of the nuts. Top with a few orange slices (leave the peel on), then add another fillet, skin-side up, to form a trout sandwich. Sprinkle with more almonds and coriander seeds. Fold up the foil sheets and grill over high heat until the fish is just cooked through and the almonds are toasted, 8 to 10 minutes. Carefully loosen the almond crust from the bottom of the foil with a spatula.