Preheat your oven to 200°C (180°C fan). Line a baking sheet with parchment paper and spread the croutons out in a single layer. Bake for 10-12 minutes, or until golden brown and crispy, stirring occasionally. You'll know they're done when they're lightly toasted and fragrant.

In a large bowl, whisk together the olive oil, lemon juice, Dijon mustard, garlic powder, salt, and pepper to make the dressing. The dressing should be smooth and emulsified, with a thick and creamy texture.

Add the chopped romaine lettuce to the bowl and toss to coat with the dressing. The lettuce should be evenly coated, with no dry spots.

In a separate bowl, combine the diced chicken breast, grated parmesan cheese, and chopped croutons. The mixture should be well combined, with the cheese and croutons evenly distributed throughout the chicken.

Add the chicken mixture to the bowl with the lettuce and toss to combine. The salad should be well mixed, with all the ingredients evenly distributed.

Cover the bowl with plastic wrap and refrigerate for at least 30 minutes to allow the flavours to meld. The salad should be chilled and refreshing, with a tangy and savoury flavour.

Just before serving, top the salad with diced hard-boiled egg, if using. The egg should be sliced into thin wedges, with a creamy and tender texture.