Preheat oven to 450°F. Scrub potatoes, dry well and pierce several times with a fork. Microwave for 4 minutes on high. Turn potatoes over and cook for 4 more minutes. Turn again, cook on low for 2 minutes, turn and cook another 2 minutes. Transfer potatoes to a work surface and cover with a bowl. Let sit for 5 minutes.
Slice a 1/4-inch "lid" off top of each potato; discard. With a small spoon scoop out flesh, leaving a shell with a 1/4-inch "wall" of flesh.
Mix scooped-out potato with butter, salt, pepper and milk in a large bowl. Mash with a fork until blended (mixture should be chunky). Stir in bacon, peas and 1 cup cheese. Fill potato skins with equal amounts of potato mixture. Top with remaining cheese and bake until cheese has melted and filling is warmed, about 10 minutes.