Preheat oven to 425°F. Line two baking sheets with parchment paper and lightly coat with cooking spray.
In a shallow bowl, whisk together eggs and milk until well combined.
In another shallow bowl, mix together panko breadcrumbs, grated Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper.
Pat zucchini slices dry with paper towels to remove excess moisture. Dip each slice first into the egg mixture, letting excess drip off, then coat thoroughly in the Parmesan breadcrumb mixture, pressing gently to adhere.
Arrange coated zucchini slices in a single layer on the prepared baking sheets, making sure they don't overlap.
Lightly spray the tops of the zucchini with cooking spray to help them brown. Bake for 20-25 minutes, flipping halfway through, until golden brown and crispy.
Remove from oven and let cool for 2-3 minutes before serving. Serve warm with marinara sauce for dipping.