Preheat oven to 350°F. Coat a 2-quart square baking dish with nonstick spray; set aside. In a large saucepan, cook potatoes, covered, in enough lightly salted boiling water to cover for 10 to 12 minutes or just until tender. Drain and set aside.
For sauce, coat a medium saucepan with nonstick spray; heat over medium heat. Add 4 of the green onions and the garlic to saucepan. Cook for 3 to 5 minutes or until onion is tender, stirring frequently. Remove from heat. Add cream cheese, mustard, and sage to onion mixture. Stir until cheese is melted and smooth. Gradually add milk, stirring until smooth.
Layer half the potato wedges in prepared baking dish. Top with half the pork chops, half the red peppers, half the sauce, and half the Gruyere cheese. Repeat layers once except do not top with remaining Gruyere cheese.
Bake, covered with foil, for 20 minutes. Uncover and top with remaining Gruyere cheese. Bake 5 to 10 minutes more or until heated through and cheese is starting to brown. Let stand 10 minutes. Sprinkle with remaining sliced green onion before serving.