The secret ingredient that makes this vegan dish “cheesy”: nutritional yeast. With a savory taste that’s similar to Parmesan, it packs protein and B vitamins as well as flavor. Include spinach, tomatoes, and basil for a classic Italian combination.
Preheat oven to 425°F. Place spaghetti squash halves cut side up on a large parchment-lined rimmed baking sheet. Rub 1 tablespoon oil over squash; sprinkle with black pepper and 1⁄4 teaspoon salt. Turn squash cut side down. Roast until fork-tender, about 35 minutes. Remove from oven. Turn cut side up, and let cool 10 minutes. Using a fork, scrape squash into “noodles,” leaving shells intact.
Heat remaining 1 tablespoon oil in a large nonstick skillet over medium. Cook garlic, stirring often, until fragrant, about 1 minute. Stir in mashed beans, broth, nutritional yeast, red pepper, and remaining 1⁄2 teaspoon salt. Cook, stirring often, until just simmering, about 2 minutes. Stir in spinach and basil, and cook until just wilted, about 1 minute. Remove from heat. Fold in squash noodles until combined.
Increase oven temperature to broil. Evenly divide squash mixture among squash shells. Sprinkle with tomatoes and panko. Broil 8 inches from heat until squash noodles begin to brown, 4 to 6 minutes. Garnish with basil.