Trim the thawed calamari tubes if needed and cut them into rings about 3/4-inch thick.

In a medium bowl combine 1/2 cup milk with about 1 teaspoon kosher salt, stirring until dissolved.

Add the calamari rings to the salted milk, cover, and refrigerate for 30 minutes to mellow flavor and help tenderize.

While the calamari soaks, whisk together the flour, cornstarch, baking powder, dried oregano, black pepper, and cayenne in a large bowl until evenly blended.

Set a large colander over a bowl. Working in batches, use tongs to lift a portion of rings from the milk, gently shake off excess, then toss them in the seasoned flour mixture so each piece is well coated; transfer coated rings to the colander and repeat with the remainder.

Preheat your oven to 150°F (65°C). Line a sheet pan with a wire rack and top with paper towels to hold fried calamari and keep it warm.

Pour enough grape seed oil into a small pot to reach about 4 inches up the sides and heat it to between 350°F and 365°F (175–185°C). If you don’t have a thermometer, test the oil by dropping in one ring—large bubbling and floating indicate it’s ready.

Fry the coated calamari in small batches so the oil temperature remains steady. Gently add rings with tongs and cook until golden and crisp, about 2½–3 minutes per batch.

Remove fried rings to the prepared wire rack lined with paper towels, immediately season lightly with kosher salt, and keep them warm in the low oven while you finish frying the rest.

Transfer the finished calamari to a serving platter, finish with a squeeze of lemon, and serve right away.