Stir together cream cheese, Summer Sauce, pepper, and 1/2 teaspoon kosher salt in a small bowl until combined. Spread cream cheese mixture on 1 side of 12 thin white bread slices, toasted. Place 1 tomato slice and about 1/4 cup thinly sliced red onion on each of 6 bread slices. Sprinkle evenly with 1/4 teaspoon salt. Cover with remaining 6 bread slices. Cut sandwiches in half; serve immediately.