1 teaspoon kosher or sea salt, plus extra to taste
Freshly ground black pepper, to taste
2 garlic cloves, minced
1/4 teaspoon red-pepper flakes (optional)
1 (28-ounce) can diced tomatoes, drained
2 small zucchini (about 8 ounces total), trimmed and diced
1/3 cup minced fresh basil
1/2 cup grated Parmesan cheese
Set a steamer basket into a Dutch oven or other large pot. Fill with water just to bottom of steamer; arrange squash in basket, skin side up. Cover, set over high heat, bring to a boil, and steam until flesh is very tender, about 20 minutes.
Meanwhile, in a medium-size pan over medium heat, add olive oil. Add onion, fennel, carrot, salt, and pepper; cook until softened, about 4 minutes. Add garlic and red-pepper flakes (if using); continue cooking until onions are translucent, about 3 more minutes. Add tomatoes and zucchini; lower heat to a simmer. Cook 20 minutes, stirring occasionally. Stir in basil. Taste sauce and add more salt if needed.
When squash is done cooking, remove it from pot and let cool until it's safe to handle. Use a fork to scrape the flesh into the pan; it will form strands. Toss gently to coat. Transfer to a bowl and top with cheese. Serve hot.