Preheat. Heat the oven to 375 degrees F and line a baking sheet with parchment. Season the bread. Toss the bread cubes with 3 tbsp olive oil, parsley, garlic, 1/4 tsp salt, and pepper until evenly coated.
Bake. Spread on the baking sheet and bake 15 to 20 minutes, stirring once, until golden brown and crisp. Marinate. Mix 3 tbsp olive oil, 2 tbsp lemon juice, zest, garlic, 1/4 tsp salt, and pepper. Coat the chicken and let it sit 15 to 30 minutes.
Sear. Cook the chicken in a hot skillet over medium high heat 6 to 7 minutes per side until it reaches 165 degrees F.
Slice. Rest the chicken for 5 minutes, then slice thinly.
Make the dressing. Whisk the mayonnaise, buttermilk, 3 tbsp Parmesan, garlic, lemon juice, Dijon, Worcestershire, and pepper until smooth.
Toss. Combine the romaine, chicken, and croutons with the dressing and top with the remaining Parmesan.