Preheat the oven to 425°F (218°C) and coat a 2-quart baking dish with cooking spray.
Heat 1 teaspoon olive oil in a large nonstick skillet over medium-high heat.
Add the sliced mushrooms, chopped onion, and chopped red bell pepper; sauté about 4 minutes until tender.
Add the chopped spinach, chopped oregano, and 1/4 teaspoon black pepper; sauté 3 minutes until the spinach wilts.
Place the 16-ounce carton cottage cheese in a food processor and process until very smooth.
In a large bowl combine the sautéed vegetable-spinach mixture, smooth cottage cheese, 4 cups hot cooked penne, 2 cups shredded cooked chicken, 3/4 cup shredded cheddar, 1/4 cup grated Parmesan, 1/2 cup milk, and the can of condensed cream of mushroom soup; stir until evenly mixed.
Transfer the mixture to the prepared baking dish and smooth the top.
Sprinkle the top with the remaining 1/4 cup shredded cheddar and remaining 1/4 cup grated Parmesan.
Bake for 25 minutes, or until the casserole is lightly browned and bubbly; remove and let sit a few minutes before serving.