Whisk capers, olives, vinegar, water, and ⅛ teaspoon pepper in a large bowl. Slowly whisk in oil until combined. Add cucumber, bread, tomatoes, onion and basil.
Oil the grill: oil a folded paper towel, hold it with tongs and rub it over the rack. (Do not use cooking spray on a hot grill.) When grilling delicate foods like fish, spray the food with cooking spray before placing it on the grill.
Season both sides of salmon with salt and the remaining ⅛ teaspoon pepper. Grill the salmon until cooked through, 4 to 5 minutes per side.
Divide the salad among 4 plates and top each with a piece of salmon.
If using fresh bread, you can grill the bread slices along with the salmon and then cut them into cubes. Or, cut bread into cubes, place on a baking sheet and bake at 300°F until dry.
Ask the butcher/meat counter to skin the salmon or skin it yourself. How to skin a salmon fillet: Place salmon fillet on a clean cutting board, skin-side down. Starting at the tail end, slip the blade of a long knife between the fish flesh and the skin, holding down firmly with your other hand. Gingerly push the blade along at a 30° angle, separating the fillet from the skin without cutting through either.
Place fish on foil or use a food flipper: Fish that flakes easily requires a delicate flip on the grill. If you want to skip turning it over when grilling, measure a piece of foil large enough to hold the fish and coat it with cooking spray. Grill the fish on the foil, without turning, until it flakes easily and reaches an internal temperature of 145°F.