Brush corn with melted butter before placing corn and red onion slices on a pre-heated gas grill over medium direct heat, or indoors on a grill pan sprayed with non-stick cooking spray set over medium-high heat.
Cook corn until kernels are slightly charred, rotating one-quarter turn every couple of minutes until each side is done. Flip red onion once while the corn is cooking. Remove vegetables from heat and slice kernels from cob with a sharp knife. Discard cobs and transfer onions and corn kernels to a largesalad bowl and set aside.
Add tomatoes, avocado, fresh parsley, and lime juice to the bowl. Season with salt and black pepper, to taste, and toss gently to combine. Serve immediately with your choice of main dish. Enjoy!