2 medium (about 2 pounds each) spaghetti squash, cut crosswise into 2-inch thick rounds
1/4 cup olive oil, divided
1/2 teaspoon black pepper
1 1/2 teaspoons fine salt, divided
6 cloves garlic, chopped
1 large yellow onion, chopped (about 2 cups)
1 pound 90/10 lean ground beef
2 tablespoons tomato paste
1 (28-ounce) can whole peeled plum tomatoes
1 teaspoon dried oregano
1 teaspoon fennel seeds, optional
1/2 teaspoon crushed red pepper
1 cup (4 ounces) shredded low-moisture part-skim mozzarella
1/4 cup finely grated parmesan
Chopped fresh basil, for garnish