Preheat oven to 400 degrees F. 

Halve each squash lengthwise; slice a sliver from the rounded part of each half so it sits flat. Leaving a 1/4-inch border, scoop out seeds with a small spoon.

Place squash halves, cut side down, in a shallow baking dish. Bake for 20 minutes. 

Meanwhile, prepare filling. In a large skillet, heat oil over medium-high. Add 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 and chili powder; cook, stirring, until fragrant, 1 minute. Add turkey, cook until no longer pink, breaking up meat with a spoon. Remove from heat. 

Divide mixture evenly among squash halves.

Bake 10 minutes, remove from oven and top with cheese. Bake another 5 minutes, or until cheese is melted and brown. 

Garnish with scallion greens.