First, make the guacamole: In a mixing bowl, combine the avocado, garlic, cilantro, and juice of one lime. Mix thoroughly and season with salt and pepper.
Preheat a grill on medium high. Drizzle a bit of olive oil over the chicken pieces and then rub them with the cumin, and chili powder or cayenne. Sprinkle on some salt and pepper. Add the chicken, whole jalapenos, and onion rings to the grill. Cook the chicken for 4 to 5 minutes on each side until it's lightly charred and firm to the touch. Cook the jalapenos and onions for the same amount of time, turning them to make sure they caramelize evenly.
Serve the grilled chicken with the guac, grilled vegetables, hunks of fresh lime, and more cilantro.