The info I have heard/read has been that they are expanding to lunch in order to accomodate more guests for free dining. I'm positive this will be a character meal as they do characters at both dinner and breakfast. I would assume that the offering would either be brunch-ish or very similar to their dinner offerings. I've done a lot of character breakfast and dinners but no lunches so I'm not sure on that.
Chef Mickey's breatkfast is your typical breakfast buffet offerings: sausage, bacon , bagels, various muffins and breads, cereal, oatmeal, pancakes/waffles, eggs dishes, potato dishes, etc. For us it was just ok, though many people like the breakfast there.
Have fun!