Preheat oven to 325 degrees F. To make pumpkin serving bowls, cut off the top one-fourth of the pumpkins; discard tops; scoop out stringy pulp and seeds. (Use seeds in Toasted Pumpkin Seeds.) Place pumpkins bowls, cut side down, in 3-quart rectangular baking dish. Add 2 tablespoons water. Bake for 30 to 45 minutes or just until tender.
In a small bowl combine melted butter, brown sugar, chili powder, and cinnamon. To grill pumpkin bowls, brush inside and cut edges of pumpkins with some of the butter mixture. Set aside remaining butter mixture. Place pumpkins, cut side down, directly on the rack of an uncovered grill over medium-hot coals (for a gas grill, preheat grill 10 minutes, reduce heat to medium). Grill for 10 to 15 minutes or until browned. Remove from grill to a platter. Cover loosely with foil to keep warm.
Meanwhile, in a medium bowl toss sweet peppers and onion with cooking oil, salt, and pepper. Heat an extra-large cast iron skillet or grill wok on grill over medium-hot coals. Add vegetable mixture; cook and stir for 6 to 8 minutes until vegetables are tender. Meanwhile, in a bowl toss sweet peppers and onion with oil, salt, and pepper. Heat a 12-inch cast iron skillet or grill wok on grill over medium-hot coals (for a gas grill, use medium heat). Add vegetable mixture; cook and stir 6 to 8 minutes until vegetables are crisp-tender. Add tomatoes; cook and stir 1 to 2 minutes more or until tomatoes are heated through. Stir in reserved butter mixture (if using a grill wok, return vegetables to a large bowl before adding butter mixture). Toss gently.
To serve, place grilled pumpkin bowls on a serving platter. Spoon vegetable mixture into pumpkin bowls scooping up some of the pumpkin pulp. Sprinkle with snipped cilantro. Makes 6 side-dish servings.