Position a rack in the upper third of the oven and preheat to 450 degrees F. Toss the squash with the vegetable oil, 1 1/2 teaspoons sesame seeds and a generous pinch of salt and pepper on a baking sheet. Roast until tender, about 20 minutes.
Meanwhile, cook the rice as the label directs. Toast the remaining 1/2 teaspoon sesame seeds in a small skillet over medium-high heat until browned, 2 to 3 minutes. Pour into a small bowl. Brush the salmon with 2 tablespoons teriyaki sauce and set aside for 5 minutes.
Remove the squash from the oven and turn on the broiler. Push the squash around on the baking sheet to make 4 open spots, then add the salmon fillets. Season the salmon lightly with salt and pepper. Broil until the fish is just cooked through and the squash is lightly browned, 4 to 8 minutes, depending on the thickness of the fish.
Stir half the scallions into the rice and divide among plates along with the salmon and squash. Spoon the remaining 2 tablespoons teriyaki sauce over the salmon and sprinkle with the remaining scallions and toasted sesame seeds.