Rinse the rice in several changes of cold water, and then add to a medium saucepan with 3 3/4 cups water and 1 teaspoon salt. Bring to a boil, and then cover and reduce the heat to low. Cook, without stirring, until tender, about 15 minutes. Remove the saucepan from the heat and let stand, covered, 15 minutes more. Transfer the rice to a baking sheet. Stir together the vinegar, sugar and 1/2 teaspoon salt. Drizzle over the rice and fold in with a spatula. Let the rice cool completely (about 10 minutes in the refrigerator or 30 minutes at room temperature).
Stir together the cream cheese, carrots and spring onions.
Place a piece of plastic wrap on the work surface and lightly oil. Place 1 1/3 cups rice on the plastic wrap and, using wet hands, press into a 7-inch square. Lay a single layer of salmon over the rice, leaving a 1/2-inch border on the side nearest to you. Line one-quarter of the vegetable cream cheese along the edge of salmon closest to you. Using the plastic wrap as an aid, firmly roll the sushi up into a cylinder. Press the rice together with even pressure to form a roll. Repeat with the remaining ingredients, making 3 more rolls.
Stir together the onion flakes, sesame seeds, dried garlic and poppy seeds on a baking sheet. Roll each roll in the seed mixture. Cut each roll into 8 pieces with a wet knife. Serve with soy, wasabi and pickled ginger.