Mix the rice and 2 ⅓ cups water in a medium skillet. Bring to a boil. Reduce heat to low and simmer, covered, for 10 minutes.
Meanwhile, slice the salmon on a diagonal into four ¾-inch-thick pieces. Season with ¼ teaspoon each salt and pepper.
After the rice has cooked for 10 minutes, place the salmon on top. Cover and cook 7 minutes more.
Scatter the peas over the salmon and rice. Cover and cook until the rice and peas are tender and the salmon is opaque and beginning to flake, 3 to 5 minutes.
Mix the soy sauce, scallions, vinegar, ginger, and sugar in a small bowl. Spoon the sauce over the salmon, rice, and peas.