While doing that, melt the butter in the oil in a large skillet on medium-high heat. When butter is sizzling, add the mushrooms into pan. Toss, and then let sit and cook, tossing every couple of minutes for about 6 to 8 minutes. Add a bit of coarse salt, and black pepper. Add 2 small ladlefuls of good chicken stock to deglaze the pan, stirring to meld flavors and make a nice glaze over the mushrooms.
While still in the pan, season the mushrooms with sea salt, and add the olives and Speck. Finally, add the oregano leaves, and toss together. The mushrooms are great served warm, but they can also be great at room temperature. If not serving right away, cover the pan with foil. Just before serving, remove the foil and arrange on a nice serving platter.