In a large non-stick skillet, melt butter and saute onions, pepper, and mushrooms until browned around edges.
Add balsamic vinegar to skillet, and let it cook out the vinegar a bit, just a good 5 second.
Reduce heat to low, and add in big bunch of fresh, chopped kale and garlic. Mix the contents until the kale is fully coated with the butter, balsamic, and veggies. The kale should just be slightly warm, not wilted.
Transfer the contents of the skillet onto a plate. Grate fresh asiago (I prefer the big shreds) over the top, if desired.