Preheat oven to 375°F.
Toss the bread cubes in the ¼ cup of olive oil and spread out on a baking sheet.
Bake until toasted, about 12 - 15 minutes, stirring after about 8 minutes.
Cool completely. The croutons can be made up to a day ahead of time and kept in a sealed plastic bag.
Toss the shrimp on a baking sheet with 2 Tablespoons of olive oil and salt.
Roast for 8 to 10 minutes, just until pink and firm and cooked through. Cool and refrigerate until serving time. (For a quicker version, use already cooked shrimp.)
To serve the salad, tear lettuce into bite-sized pieces and place into a large bowl and toss with most of the dressing.
Divide lettuce among plates and top each serving with equal parts of shrimp, crab, and croutons.
Drizzle with remaining dressing.
Sprinkle with Parmesan cheese and season with freshly ground pepper.