Stir together cream cheese, lemon juice, grated onion, and salt until well blended.
Spread 1 Tbsp. of the cream cheese mixture on each bread slice.
Top with desired toppings such as fresh or blanched vegetables, thinly sliced deli meat, smoked salmon, herbs, and spices.
Cover with plastic wrap, and chill 15 minutes to 12 hours.
Trim crusts from chilled slices, and cut each slice into 2 triangles.
Serve multiple varieties together for a unique mosaic look.