In a small bowl, stir together mayonnaise, sour cream, lemon juice, dill weed, and horseradish.
Spread a little of the dill mixture over each bread slice; top with a few tomatoslices.
Evenly distribute shrimp atop tomato slices; spoon remaining dill mixture over shrimp.
Top sandwiches with avocado slices.
Garnish with dill sprigs and lemon wedges, if desired.
Eat with knife and fork.