Preheat oven to 350°F (175°C).
Heat olive oil in a large skillet over medium heat.
Add diced onion and cook until translucent, about 3 minutes.
Add minced garlic, sliced mushrooms, and chopped bell pepper. Cook for 5 minutes until vegetables are tender.
Add ground turkey to the skillet. Cook, breaking it up with a spoon, until no longer pink, about 7 minutes.
Stir in drained diced tomatoes, cream of mushroom soup, milk, Italian seasoning, salt, and black pepper. Cook for 2 minutes, stirring occasionally.
Remove skillet from heat and stir in cooked elbow macaroni and half of the shredded cheddar and mozzarella cheeses.
Transfer mixture to a 9×13 inch casserole dish and spread evenly.
Sprinkle the remaining cheddar and mozzarella cheeses evenly over the top.
Cover the casserole tightly with aluminum foil.
To freeze: Place the covered casserole in the freezer for up to 3 months.
To bake from frozen: Preheat oven to 375°F (190°C). Remove foil and cover casserole with fresh foil. Bake covered for 45 minutes, then remove foil and bake an additional 10 minutes until cheese is bubbly and golden.
Let casserole rest for 5 minutes before serving.