- Preheat oven to 375 degrees.
- For dressing, mix first 8 ingredients together and set aside until ready to use.
- To prepare scallops, cut them in half lengthwise. Steam for 3 minutes. Drain, but reserve steaming water.
- To prepare potatoes, boil potatoes until fork tender. Drain. Mix potatoes with butter, garlic, salt, and 1 cup reserved scallop cooking water. Mash or whip by hand until creamy.
- To assemble casserole, layer ½ the potatoes in bottom of a large casserole dish and top with ½ the ranch dressing followed by ½ the scallops. Sprinkle ½ of each of the cheeses. Repeat layers. Top casserole with peppers and sprinkle with chives. Bake for 25 minutes.