In a food processor, combine the beans, peppers, tahini, garlic, lemon juice, cumin, salt and cayenne pepper, if using. Blend until smooth, scraping down the sides of the bowl if needed. Season with salt, to taste. Transfer the hummus to a small bowl.
Run the tines of a fork down the length of each cucumber several times, turning to make ridges about 1/8-inch deep in the skin all the way around. Cut cucumbers crosswise into 1-inch rounds, for a total of at least 12. Using the smaller end of a melon baller or a round measuring spoon, scoop out the center of each cucumber round to form a hollow. Use a small spoon to fill each cup with hummus, mounding slightly over the top. Tuck a small fresh parsley, cilantro or mint leaf into the side of the filling as a garnish.
Arrange the cups on a platter and serve.