Line a 3 1/2- or 4-quart slow cooker with a disposable slow cooker liner. Lightly coat liner with cooking spray; set cooker aside.
In a large skillet cook potatoes in hot oil over medium heat for 8 to 10 minutes or until lightly browned and almost tender, stirring occasionally. Add squash; cook for 4 minutes, stirring occasionally. Stir in sweet pepper; cook for 2 minutes more. Remove from heat; stir in green onions.
In a large bowl combine eggs, milk, parsley, salt, and black pepper. Stir in cooked vegetables, 1 cup of the cheese, and the panko. Pour mixture into the prepared cooker. Sprinkle with the remaining 1/2 cup cheese.
Cover and cook on low-heat setting about 3 hours or until a knife inserted in the center comes out clean. Turn off cooker. If possible, remove disposable liner from cooker. Cool for 15 to 30 minutes before serving.