Preheat the oven to 400°F.
Prepare the croutons. Arrange the bread on a baking sheet. Toss with garlic, salt, pepper, and olive oil. Bake for 8-10 minutes, tossing halfway, until golden and slightly chewy. Transfer the croutons to a large bowl.
Make the dressing. Whisk together mayonnaise, Greek yogurt, lemon juice, Dijon mustard, Worcestershire, an anchovy fillet, garlic, and pepper in a medium bowl. Adjust seasoning as needed. Mix ¼ cup of the dressing with ¼ cup grated Parmesan in a small bowl. Set aside the remaining dressing.
Bake the salmon. Pat salmon fillets dry and season lightly with salt and pepper. Generously brush the fillets with the Parmesan dressing. Place them on the baking sheet and sprinkle with ¼ cup Parmesan. Bake at 400°F for 12 minutes, or until the salmon is cooked through and golden on top.
Assemble the salad. In a large bowl, toss lettuce, croutons, and onion with some dressing using tongs. Divide the salad onto plates and top each with a salmon fillet. Serve immediately.