Slow Cooker Stuffed Zucchini

2 large zucchini, trimmed and halved lengthwise

4 ripe tomatoes, cored

¼ cup olive oil

¾ teaspoon salt

½ teaspoon ground black pepper

1 teaspoon crushed garlic

4 fresh basil leaves

1 teaspoon dried Italian herb seasoning

1 teaspoon white sugar

3 tablespoons olive oil

1 onion, diced

1 pound bulk sweet Italian sausage

¼ cup grated Parmesan cheese

1 cup grated mozzarella cheese

Scoop out flesh from the zucchini halves, leaving shells about 1/8 inch thick. (Zucchini flesh may be saved for another use.)

Place tomatoes, 1/4 cup olive oil, salt, black pepper, garlic, basil leaves, Italian herb seasoning, and sugar into a food processor and pulse until blended, about 1 minute. Set mixture aside.

Heat 3 tablespoons olive oil in a large skillet over medium heat; cook and stir onion until translucent, about 5 minutes. Add sausage to skillet and cook, stirring often, until browned and crumbly, about 10 minutes. Stir in the tomato mixture and heat until simmering; stir in Parmesan cheese.

Place hollowed-out zucchini shells into the bottom of a large slow cooker, trimming them to fit if necessary. Spoon the sausage mixture into the shells, cover the cooker, and cook on High until tender, about 6 hours. Remove cover and spread a layer of mozzarella cheese over each stuffed zucchini. Cover and cook on High until cheese has melted, about 10 more minutes.