In a small bowl, toss together the salmon and teriyaki sauce. Let marinate for 10 minutes.
While the fish is marinating, preheat the broiler to high. Toast the split sides of the rolls under the broiler until golden brown. Reserve.
In a small bowl, stir together the mayonnaise, wasabi powder and vinegar. Reserve.
Place a large skillet over medium-high heat with the oil. Add the marinated salmon to the pan, reserving the teriyaki sauce it was marinated in, and sear for 1 minute. Carefully turn the salmon and continue cooking for 1 minute more. Add 2 tablespoons of water to the reserved teriyaki sauce, then add it to the skillet with the salmon. Continue cooking the salmon until the sauce has reduced and thickened to a glaze, about 2 minutes. Remove the skillet from the heat and gently spoon the glaze over the pieces of salmon.
To assemble the sliders, spread a little wasabi cream on the bottom of each toasted slider. Pile the sliders up with a few leaves of spinach, the seared salmon and a few pieces of pickled ginger. Cap with the toasted bun top and serve warm.
If you want to use a whole wheat roll, see if your grocery store has whole wheat potato rolls. I know they're a bit indulgent, but the soft potato rolls are ideal here, as the soft texture of the salmon won't hold up to a crusty bakery roll. Bulk up the vegetables in this meal by serving these sliders with a simple salad of 1 thinly sliced seedless cucumber tossed with 2 tablespoons soy sauce, 2 tablespoons honey, 2 tablespoons rice wine vinegar and 1 teaspoon sesame oil.