Add 2 cups water to a small saucepan. Bring to a boil. Remove from heat and add 1/2 cup sun dried tomatoes. Let sit to re-hydrate for about 5 mins. Drain & run some cool water over tomatoes.
Slice tomatoes into thin strips. Add to bowl, along with the feta, basil, oregano, garlic & 1/2 of the ground pepper. Mix well.
Butterfly the chicken to stuff, then using a meat mallet, pound to flatten a bit. Spoon feta mixture into chicken. Close up chicken, spread some butter over the top & sprinkle with remaining black pepper. Wrap tightly in foil.
Place on a hot BBQ grill for 1/2 hour, or until done, flipping once or twice during cooking (or you can bake in a 425 degree oven)
Carefully open foil packs. Place on a serving plate & slice into medallions. Serve.