Stuffed Zucchini with Chicken Sausage

2 zucchini, ends trimmed
3 tablespoons olive oil
2 links Italian-style chicken sausage, casings removed
2 teaspoons crushed red pepper flakes (optional)
salt and ground black pepper to taste
½ sweet onion, chopped
3 cloves garlic, chopped
1 can 14.5 ounce whole peeled tomatoes, drained and chopped
½ cup dry bread crumbs
¼ cup grated Parmesan cheese
1 tablespoon chopped fresh basil

Preheat oven to 375 degrees F (190 degrees C).
Cut a lengthwise 3/4-inch thick slice from each zucchini.
Retain the lengthwise slices. With a spoon, scoop out the flesh, leaving a shell intact all around the zucchini.
Discard or save the flesh for another use. Chop up the retained lengthwise slices of zucchini.
Heat the olive oil in a skillet over medium heat, and cook the chicken sausage, breaking the meat up as it cooks,
until the sausage has begun to brown, about 8 minutes.
Sprinkle in the crushed red pepper flakes, and season with salt and black pepper.
Stir in the chopped zucchini, onion, and garlic, and cook until the onion is translucent, about 5 minutes.
Scrape the sausage mixture into a bowl, and stir in the tomatoes, bread crumbs, Parmesan cheese,
and basil until the stuffing is thoroughly combined.
Lightly stuff the zucchini boats with the stuffing, place the zucchini into a baking dish,
and bake until thoroughly heated through and beginning to brown on top, about 30 minutes.