Remove stems from collard leaves with a paring knife and lay the two halves back together, slightly overlapping. Set aside remaining chopped vegetables. Combine almond butter and all remaining ingredients in a blender and blend until smooth, adding more water if necessary. Transfer the dipping sauce to a small serving bowl.

Lay two collard halves out on the counter with the middle slightly overlapping so it looks like they are put back together after the stems were removed. Sprinkle about 1/4 cup of each vegetable along one end of the collard leaves, then roll up tightly starting from the filled end. Secure with a toothpick and arrange attractively on a serving platter. Scatter freshly picked nasturtium blossoms around for garnish. Place dipping sauce in center of the platter and serve.