Season chicken well on both sides. drizzle olive oil over chicken and make sure each side is coated.
NOW here is the secret! use real wood lump charcoal or at least use some wood chips on the charcoal. this is important and effects the over all flavor if you don't use some sort of wood. right after you remove the chicken from the grill place a little of the goat cheese on each piece and let get warm from the heat off the chicken.
lightly brush the cut parts of the ciabatta bread and grill until lightly browned, this helps your bread not get soggy from the sauce.
grill for 2-3 minutes per side.
make sauce: 1 Tbsp of butter in a sauce pan and saute the onion and garlic over a med-low heat until translucent and careful not to brown! add wine and lemon juice. bring to a boil and let cook on med-high heat for 3 minutes. remove from heat. add the remaining butter pieces and continuously stir until they are melted. now add the basil and tomato and give a quick stir. let sit on stove while making sandwiches. the longer it sits the more solid it will become again. so do the sauce last.
assembly: bottom bun place the spinach in a thick layer, top with chicken spoon a few spoon fulls of the sauce over the chicken and put top part of bread on. serve immediately.