Heat 2 tablespoons oil in a large saucepan over medium-high heat. Place beef in the saucepan and cook until evenly brown. Mix in the water, potatoes, carrots, green bell pepper, garlic, onion, salt and pepper. Bring to a boil. Reduce heat and simmer approximately 2 hours.
Dissolve the bouillon into the beef mixture. Stir in the tomatoes.
Preheat oven to 325 degrees F (165 degrees C).
Cut top off the pumpkin and remove seeds and pulp. Place the pumpkin in a heavy baking pan. Fill the pumpkin with the beef mixture. Brush outside of the pumpkin with remaining oil.
Bake in the preheated oven 2 hours, or until tender. Serve the stew from the pumpkin, scraping out some of the pumpkin meat with each serving.