Bring a medium saucepan of water to a gentle simmer and season generously with salt. Add the shrimp and cook for 2 to 3 minutes, until pink and curled into a loose "C" shape.
Immediately drain the shrimp and transfer to a bowl of ice water. Let cool for 1 to 2 minutes, then drain again and pat dry. Chop into bite-size pieces.
Add the sliced almonds to a dry skillet over medium heat. Toast for 3 to 4 minutes, stirring often, until light golden and fragrant. Remove from heat and set aside.
Dice the apple and celery into pieces roughly the size of the shrimp. If prepping ahead, toss the apple with a little of the reserved lemon juice.
In a small bowl, whisk together the mayonnaise, lemon juice, lemon zest, Dijon mustard, salt, and pepper until smooth.
In a large bowl, combine the shrimp, apple, celery, minced shallot, and dill. Pour the dressing over and toss gently to coat.
Fold in the toasted almonds just before serving. Chill for at least 15 minutes, then serve over lettuce leaves with extra almonds on top.