Avocado Sandwiches

1 ripe avocado, halved, pitted and thinly sliced
Juice of 1 lemon
2 T. unsalted butter
1 c. microgreens
¼ c. California walnuts, coarsely chopped
6 slices good-quality white bread

Sprinkle lemon juice over avocado slices; let drain. Thinly butter each slice of bread on one side, spreading butter to edge of crusts. Trim crusts from bread slices. Divide microgreens into 6 portions and sprinkle on bread slices. Divide avocado slices into 6 portions and layer neatly over microgreens on top of each bread slice. Sprinkle walnuts over avocados on bread slices. Place on serving dish, cover with slightly dampened paper towel, and seal with saran wrap; place in refrigerator until ready to serve.