Lightly rinse the beans, and add them to a pot of cold water. Bring to boil and let it cook for 40 - 45 minutes until the beans are soft. DO NOT ADD SALT. Drain and set aside.
While the beans is cooking, peel and chop the avocado into bite-sized chunks. Rinse and dice the red bell pepper. Finely chop the cilantro.
If using sweetcorn-on-the-cob, shuck the cob using a sharp knife. Then place the sweetcorn in boiling water, to which a pinch of sugar has been added. Allow the water to come back to a boil and then wait 3 - 5 minutes before removing the corn from the water. Drain excess water, add a dollop of butter to the kernels and set aside. Skip this step if using canned or frozen sweet corn.
Place all the ingredients together in a large glass bowl. Squeeze the juice of half a fresh lemon, and two teaspoons of olive oil over the salsa. Sprinkle some salt and pepper to your taste. Mix well together and enjoy.