Preheat oven to 300 deg. Combine all ingredients in a large roasting pan or casserole dish. Place in oven and cook, uncovered, for 4 hours. The pumpkin, chayote and tomatoes will cook down to a thick sauce. Stir every 30 minutes. Add more stock if necessary. Serve hot. Per serving: 316 cal; 11 g prot; 222 mgsod; 52 g carb; 9 g fat; 0 mg chol; 53 mg calcium