Rinse the quinoa under cold water until the water runs clear. Drain well then transfer to a small pot. Add water, dashi powder, and dried kelp. Bring to a boil over medium heat then cover with a lid. Reduce the heat to low and simmer for 15 minutes. You can also follow the package instructions for the recommended cook time.
Prepare the miso sauce by combining white miso, soy sauce, sake, mirin, and sugar. Mix until well combined.
Season the salmon with salt and pepper then coat all sides in all-purpose flour. Make sure to shake off the excess flour then set aside.
Heat olive oil in a pan over medium heat. Carefully add the salmon to the pan skin side up. Cook for 2 to 3 minutes then flip and cook for another 2 minutes. The cooking time will depend on the thickness of the salmon.
Push the salmon to the side then add the sliced mushrooms. Once the mushrooms have softened, about 1 minute, pour the miso sauce over the mushrooms.
Remove the salmon from the pan. Cook the sauce down until it slightly thickens.
To serve, plate the quinoa and salmon. Spoon the miso mushroom sauce on top of the salmon. Add toppings of your choice including assorted greens, quick pickled cucumbers, and avocado.