Clean the Portobello mushrooms by gently wiping them with a damp cloth. Remove the stems and set aside.
In a shallow bowl, combine the flour, garlic powder, onion powder, paprika, salt, and pepper.
In another bowl, whisk the eggs until smooth.
Place the breadcrumbs in a third shallow bowl.
Coat each mushroom cap in the flour mixture, dip in the eggs, then dredge in the breadcrumbs, pressing gently to ensure an even coat.
Heat oil in a large frying pan over medium-high heat (350°F/175°C).
Fry the mushroom caps in batches for about 3-4 minutes per side, or until golden brown and crispy.
Transfer the mushrooms to a paper towel-lined plate to drain excess oil.
Serve immediately with your favorite dipping sauce or as a sandwich filling.