Preheat the oven to 375°F (190°C).
Cook the cannelloni (or manicotti/lasagna sheets) in a large pot according to package directions until al dente, then drain and set aside.
In a large mixing bowl, combine the ground turkey with garlic powder, black pepper, dried sage, crushed red pepper flakes, fennel seeds, dried oregano, and salt; mix thoroughly.
Heat a large skillet over medium heat. Add the seasoned ground turkey and cook, breaking into small pieces, until no longer pink throughout.
Drain any excess fat from the skillet, then stir in 1 cup of the tomato-basil sauce and remove the skillet from the heat.
Carefully cut each cannelloni lengthwise (or open shells/sheets as needed). Spoon the turkey filling down the center of each piece and press the pasta closed or roll to enclose the filling.
Place the filled cannelloni in a baking dish. Pour the remaining tomato-basil sauce evenly over the top and cover the dish tightly with foil.
Bake in the preheated oven for 20 to 25 minutes, until heated through and bubbly.
Remove from the oven, garnish with torn basil leaves if desired, and serve.