Pound chicken breasts, or butterfly, until 1/2-inch thick.
Brush both sides with olive oil and season with salt and pepper.
Combine butter and hot sauce in a small sauce pan and heat until butter is melted.
Grill chicken 5-6 minutes per side over medium heat, or until cooked through and the internal temperature is 165 degrees F.
Brush hot sauce mixture over both sides of the chicken while grilling.
With a clean brush, brush both sides of the red onion rounds with olive oil and season with salt and pepper. Grill over medium heat until the onion begins to soften and is slightly charred on both sides.
Brush cut side of the ciabatta rolls with olive oil. Grill until golden brown.
Assemble the sandwiches by layering the lettuce, grilled onion, chicken, Ranch aioli and crumbled blue cheese. Finish with top of ciabatta roll, cut in half and serve.