Begin by slicing the large, firm portobello mushrooms into strips approximately 1/2-inch wide. Place the mushroom strips on a paper towel to absorb excess moisture.

Create a breading station with three bowls: one with panko breadcrumbs, one with a mixture of flour, onion salt, black pepper, smoked paprika, and garlic powder, and one with beaten eggs.

Dip each mushroom strip into the seasoned flour mixture, then into the egg mixture, and finally coat with panko breadcrumbs.

Heat vegetable oil in a cast iron pan or Dutch oven to about 370°F.

Carefully place the coated portobello mushroom fries into the hot oil in small batches, frying until golden brown.

Use a slotted spoon to drain the fried mushrooms on paper towels and garnish with minced parsley before serving.