Place tofu on several layers of heavy-duty paper towels; let stand 20 minutes. Cut into 1/2-inch cubes.
Heat oil in a medium saucepan over medium heat. Add tofu and seeds; sauté 3 minutes. Remove tofu mixture from pan. Add quinoa to pan; cook 3 minutes, stirring frequently. Add stock and salt; bring to a boil. Cover, reduce heat, and simmer 20 minutes. Place in a large bowl. Add tofu mixture, green onions, soy sauce, and pepper; toss.