1 Preheat the oven to 450°F. Tear four 12x18-inch sheets of parchment paper.,

2 Combine the onion, tomatoes, and 2 teaspoons of the oil in a bowl.,

3 Arrange one sheet of parchment so that the long side is closest to you. Fold it in half, matching short end to short end; then open it like a book. Place one-fourth of the tomato mixture in the center of the right half of the parchment sheet. Place a halibut filet next to the tomato mixture and one-fourth of the asparagus next to the halibut.,

4 Drizzle with 1 teaspoon oil and 1-1/2 teaspoons lemon juice, and top with 2 sprigs fresh thyme. Season evenly with salt and pepper. Fold the parchment over the filling, then tightly crimp the edges to form a packet. Repeat with the remaining ingredients.,

5 Place the packets on a large baking sheet and bake in the center of the oven until the packets are puffed. 11 to 12 minutes.,

6 Remove from the oven and transfer each packet to a plate. With the tip of a sharp knife, carefully cut and "X" into the top of each packet to allow the steam to escape. Then fold back the parchment and serve immediately.