Fill a large Dutch oven or skillet with 1/2 inch of oil and heat over medium-high heat until a deep-fry thermometer registers 350 degrees F. Line a plate with paper towels.
Slice the green tomatoes 1/2 inch thick. Whisk together the flour, cayenne, garlic powder and 1/2 teaspoon salt in a shallow dish. Whisk together the eggs and milk in another shallow dish. Put the panko in a third shallow dish. Dredge each tomato slice in the flour, then egg, then panko.
Fry the green tomatoes, turning, until golden, 3 to 5 minutes. Transfer to the prepared paper towel-lined plate. Serve the fried green tomatoes with ranch dressing.
Courtesy of Food Network Magazine, Photograph by Ryan Dausch