2 teaspoons extra-virgin olive oil
6 ounces baby spinach, chopped
1/2 cup chopped onion
3/4 teaspoon salt, divided
12 ounces 93%-lean ground beef
1/2 teaspoon garlic powder, divided
2 tablespoons all-purpose flour
2 12-ounce packages frozen winter squash puree, thawed
1 tablespoon tomato paste
1/3 cup finely shredded Parmesan cheese
1 cup reduced-sodium beef broth
Position rack in upper third of oven; preheat broiler.
Heat oil in a large skillet over medium-high heat. Add onion and cook, stirring, until beginning to soften, about two minutes.
Reduce heat to medium, stir in beef, flour and tomato paste, and cook, stirring, until the beef is mostly browned, about 3 minutes. Add broth, scraping up any browned bits with a wooden spoon.
Bring to a boil and cook, stirring occasionally, until the broth is the consistency of thick gravy, about 4 minutes. Stir in spinach, 1/4 teaspoon salt and 1/4 teaspoon garlic powder; cook until the spinach is just wilted, about one minute.
Place squash in a fine-mesh sieve and gently press on it to extract excess liquid. Transfer to a bowl. Stir in the remaining 1/2 teaspoon salt and 1/4 teaspoon garlic powder. Divide the meat mixture among four 10-ounce broiler-safe ramekins.
Top each with about 1/2 cup of the squash. Place the ramekins on a baking sheet.
Broil until heated through and bubbling around the edges, about 10 minutes. Sprinkle with cheese and broil until it is just melted, about 3 minutes more.