Cook the quinoa as the label directs. Meanwhile, whisk 1/3 cup each soy sauce and mirin with three-quarters of the garlic, the ginger and honey in a medium bowl. Add the salmon and turn to coat. Let marinate at room temperature, 15 minutes.
Stir the scallions and the remaining 2 tablespoons soy sauce into the quinoa. Cover and set aside.
Heat a large nonstick skillet over medium-high heat. Add 2 tablespoons vegetable oil. Add the bok choy and cook until the leaves start wilting, 3 to 4 minutes. Add the remaining garlic and the mushrooms and cook, stirring occasionally, until softened, about 5 minutes. Add the remaining 2 tablespoons mirin and the lemon zest; toss to coat. Transfer the vegetables to a bowl.
Wipe out the skillet and increase the heat to high. Add the remaining 1 tablespoon vegetable oil. Add the salmon and about one-third of the marinade to the skillet (discard the remaining marinade). Cook until the salmon is golden brown and cooked through, 3 minutes per side. Top each serving of quinoa with the vegetables, salmon and more scallions. Serve with lemon wedges.