Preheat the oven to 375°F (190°C).
Cook the cannelloni or pasta shells according to package directions until al dente; drain and set aside.
In a large mixing bowl, combine the cooked ground turkey with garlic powder, black pepper, dried sage, crushed red pepper flakes, fennel seeds, dried oregano, and salt; mix until evenly seasoned.
Heat a large skillet over medium heat and add the seasoned turkey. Cook, breaking into small pieces, until no pink remains.
Drain any excess fat from the skillet, then stir in 1 cup of the tomato-basil sauce and remove from heat.
Cut each cannelloni or shell lengthwise and spoon a portion of the turkey mixture into the center, then press the pasta back together to enclose the filling. Repeat until all are filled.
Spread the remaining tomato-basil sauce in the bottom of a baking dish, arrange the filled cannelloni on top, then cover with any remaining sauce.
Cover the dish tightly with foil and bake for 20 to 25 minutes, until heated through and bubbly.
Remove from the oven, garnish with torn basil leaves if desired, and serve.