Heat oven to 450°F and arrange rack in the upper third.
Combine flour, oregano, and paprika in a shallow dish. Season with salt and pepper and whisk to combine.
Crack eggs into another shallow dish. Add 1 tablespoon of water and season with salt and pepper. Whisk until smooth.
Place panko in a third shallow dish. Season with salt and pepper and mix to combine.
Dip the avocado slices in the flour mixture, turning to coat all sides. Then place in the egg mixture, turning to coat, then finally the panko, pressing gently to coat all sides. Place in a single layer on a baking sheet.
Drizzle avocado slices with the olive oil then place on the top rack of the oven. Bake until golden and crispy, about 10-15 minutes turning halfway through.
Meanwhile, combine all the ingredients for the Harissa Ranch in a medium bowl. Whisk until smooth. Taste and add more salt or lemon juice as needed.
Serve avocado fries hot with ranch dip and lemon wedges for squeezing.