Start with firm, ripe gold rush squash.
Heat oven to 400 degrees, with rack set in the top third.
Halve each squash lengthwise; slice sliver from the rounded part of each half so it sits flat. Leaving a ¼-inch border, scoop out halves with a small spoon; roughly chop flesh, and reserve. Place squash halves, skin side down, in a shallow baking dish. Season with salt and pepper, and set aside.
In a large skillet, heat oil over medium-high. Add ½ of the reserved chopped squash (save the rest for another recipe or enjoy it raw), bell pepper, scallion whites, and garlic; season with salt and pepper. Cook, stirring occasionally, until bell pepper begins to soften, 3 to 4 minutes. Add tomato paste, Mrs. Dash and chili powder; cook, stirring, until fragrant, 1 minute. Add beef; cook until no longer pink, breaking up meat with a spoon, 2 to 3 minutes. Remove from heat. Stir in corn and ¼ cup Parmesan; season with salt and pepper.
Dividing evenly, spoon mixture into squash halves. Sprinkle with remaining 2 tablespoons Parmesan. Cover with aluminum foil, and bake until squash is tender, 30 to 35 minutes. Uncover, and bake until top is browned about 7-10 minutes more. Garnish with scallion greens.