Cut the florets from the cauliflower core. Pulse half at a time in food processor, in 1 second pulses until it's minced into fine bits, just a bit larger than couscous (you should have about 4 cups).
Place cauliflower on a several sheets and layers of paper towels, then wrap and press to remove some of the excess liquid. Set aside.
Heat oil in a 12-inch non-stick skillet over medium-high heat. Add onions and garlic and saute 30 seconds. Add in cauliflower "rice" and saute 6 minutes.
Add in corn and black beans, season with salt to taste and warm through, about 1 - 2 minutes. Remove from heat.
Add tomatoes, avocado, cilantro, lime juice and lime zest and gently toss. Serve warm.
Recipe source: Cooking Classy
If you'd like to make the rice into chicken burrito bowls - pound 4 (6 oz) chicken breasts to an even thinness. Brush both sides lightly with olive oil and season with S & P. Season both sides with (total) 1 tsp ancho chili powder, 1 tsp ground cumin, 1 tsp garlic powder, 1/8 tsp sugar (for a better char). Grill on preheated 425 degree grill, about 4 minutes per side. Let rest 5 minutes on a plate then cut int cubes. Serve with this "rice", top with Queso fresco cheese if desired.