Slice all of the vegetables thinly using a mandoline or very sharp knife to about 1/16" slices for each. Place bread slices out onto a large cutting board. Spoon a heaping Tablespoon of the spicy black bean hummus mixture onto each slice and spread evenly. Next add feta cheese crumbles to four of the slices, reserving the other four slices until the end to be used as tops.Place a thin layer of red peppers onto each of the four pieces with the feta cheese, followed by a layer of cucumbers, beets, onions, red cabbage, spinach, and herbs. Top each of the four sandwiches with the reserved pieces to form sandwiches. Slice each one in half and serve.Drain the black beans by half and place into a food processor. Next add in the tahini paste, jalapeno, lime juice, garlic, cumin powder, and salt and pulse together until well combined and smooth. Use this as a sandwich spread or a dip with your favorite vegetables or chips.