Measure cauliflower florets and place into food processor. (Depending on the size of your food processor, you may want to do this in 3 or more batches.)
Pulse until cauliflower is finely chopped (about the size of small grains of rice). You should have about 5 cups finely chopped cauliflower.
To serve, place cauliflower on large serving platter or dish. Top with black beans, diced onion, and tomatoes. Sprinkle cilantro over all. Serve with guacamole on the side (and sour cream if desired). Serve immediately.
Notes
1. If desired, black beans can be seasoned with granulated onion, cumin, granulated garlic, and salt.2. Because some prefer to buy their guac and sour cream rather than making it, I omitted these from prep time calculations. If you are making your own, adjust the prep time accordingly.