Guess I should have come over to help you. I always wear ear protectors and safety glasses. Gloves are optional. You cut inside the soap dish first, controlling the depth of the cut, cutting around the perimeter but inside the grout line.
Then, because you are now a certified angle grinder professional, you can work outward, trimming the tile away as you get closer and closer to the grout line. If you are REALLY good, the last bit will fly off, leaving a clean edge. Being very careful, you can even trim the residual face of the wall by gently moving side to side. If you suck, well, you bash a hole through the greenboard and you are left with a crappy hole in the wall where water can get in someday ...
We all make mistakes. Not meaning to offend you.
Have never used the "Smart Tile" (
http://www.thesmarttiles.com/en_us/ ) Are you planning on retiling the entire shower or just the new and quite fashionable hole you created?
Actually, if you are going to a new look, maybe you should remove that entire horizontal course and install an accent band. By the 2nd or 3rd tile, you ought to be able to do it without punching a hole in the greenboard!
Whatever ... Here is a video which gives you the basics for fixing a drywall hole.
https://www.youtube.com/watch?v=K37G2j0K8BA
You have to do your best to square up that irregular hole BUT LEAVE A LIP FOR SCREWS. Cut a piece of greenboard for the hole, and hope you have enough old drywall lip to hold the backing board.
Actually your biggest problem is waterproofing the hole. There are elastomeric paint-on coverings (RedGard) which are great but not available in small quantities. Do some checking because you really need to seal that patch before tiling. Once you do that, you can tile with anything that fits your sense of interior design ... BUT make sure you apply grout sealer (multiple coats) to prevent water seeping into the new grout lines.