Cook turkey in a large skillet over medium heat, sprinkle with sage, red pepper flakes, black pepper and salt to taste. Break turkey up into chunks while cooking, continue cooking until it has lost its pink color and is cooked through. Drain and set aside.
In a medium non-stick skillet, on medium-low heat, add oil and cook onion rings until they begin to caramelize, about 10 minutes. Add mushrooms and continue cooking until mushrooms release moisture, about 5 additional minutes. Drain liquid.
Cook penne according to instructions of the box. Note: Approximately 1-1/2 cups uncooked pasta equals 4 cups cooked.
Combine in a large mixing bowl marinara, cooked penne, cooked turkey and basil, spread into a 9"x13" casserole dish. Evenly distribute remaining ingredients over penne, top with mozzarella. Bake uncovered 20-25 minutes or until cheese is hot and bubbly.
Tip: Marinara (no sugar added) - Ragu has a lite sauce if you're on a budget (who's not?); if splurging try Amy’s Organic Marinara Pasta Sauce