Prepare lemon aioli by whisking together mayonnaise with lemon zest, lemon juice, and tabasco Season with salt and pepper.
Combine calamari with buttermilk, stirring to combine. Let sit in the refrigerator for 20 minutes. Drain calamari.
Preheat frying oil to 375 degrees F.
Combine flour with cornstarch, paprika, salt, pepper, onion powder, and cayenne in a large bowl. Dredge calamari in seasoned flour, tossing evenly to coat and shaking excess.
Carefully drop a handful of the calamari into the hot oil. Cook until golden brown, about 1-2 minutes. Remove with a slotted spoon and transfer to a paper towel-lined baking sheet. Repeat with remaining calamari.
Transfer calamari to serving platter and sprinkle parsley on top. Serve with lemon wedges and lemon aioli.