Place apricots and prunes in bowl, and cover with 1 cup boiling water. Soak 2 hours, or overnight. Drain, and coarsely chop fruit, reserving liquid.
Preheat oven to 350°F. Coat baking sheet with cooking spray. Cut circular opening in squash tops, and reserve tops. Cut small slices off bottoms of squash so they stand up straight. Scoop out and discard seeds and fiber from squash. Rub outsides of squash shells and lids with oil, and place on prepared baking sheet.
Heat 1 Tbs. oil in large saucepan over medium heat. Add onion, garlic, and oregano; sauté 2 to 3 minutes. Add bell pepper and tomatoes and juice; cook 2 to 3 minutes. Add potato, sweet potato, and reserved apricot-prune soaking liquid, and bring to a boil. Reduce heat to medium-low, cover, and simmer 15 to 20 minutes, or until potatoes are almost soft. Add corn and apricot-prune mixture, and simmer 2 to 3 minutes more. Add beans, and season with salt and pepper, if desired. Simmer 5 minutes more.
Ladle 1 cup stew into each hollowed squash; place lid on top. Bake 60 to 90 minutes, or until fork can easily pierce through squash.