Toss calamari with buttermilk in a non-reactive bowl, cover and let marinated in the refrigerator for 2 hours.
Make topping by heating olive oil over medium heat in a medium skillet. Add peppers, sun-dried tomatoes, scallions, fresh ginger, and wasabi and saute until peppers are tender and flavors integrate. Remove from heat and set aside.
Drain marinated calamari through a strainer or colander. Heat canola oil in deep-fryer to 375 degrees F (or as deep-fryer manufacturer directs for similar foods). To make tempura, mix flour, cornstarch, baking powder, and salt and pepper in a bowl. Dredge sliced calamari in the dry mix, then set aside briefly. Add seltzer in a stream to the tempura mix while whisking constantly to make into a batter. Dip calamari into the batter or ladle batter over the calamari, and place into the deep-fryer basket, frying for a minute or two until golden brown. Drain on paper towels.
Finish by adjusting seasoning in topping with salt and pepper. Serve topping over fried calamari and squeeze lemon and lime juice over.