Slice chicken breasts horizontally into thin cutlets (about 1/2 inch thick). Season both sides with salt and pepper.
Set up breading station: In a shallow bowl, mix flour with garlic powder, paprika, cayenne (if using), and a pinch of salt. In another bowl, beat eggs. In a third bowl, place panko.
Dredge each cutlet in flour mixture, shaking off excess. Dip into egg, then coat with panko, pressing gently to adhere.
Heat olive oil in a large skillet over medium-high heat. Cook chicken in batches (do not overcrowd) for 3-4 minutes per side until golden brown and cooked through (internal temp 165°F). Transfer to a paper towel-lined plate. Let rest 2 minutes, then slice into strips.
In a small bowl or jar, whisk together olive oil, vinegar, mustard, honey, garlic, parsley, salt, and pepper until emulsified.
In a large bowl, combine romaine, cucumber, tomatoes, and red onion. Drizzle with dressing and toss to coat. Divide among plates, top with crispy chicken strips, and serve immediately.