Preheat oven to 375°F.

Cook sausage in a large pan over medium-high heat until no longer pink. Stir often to crumble the sausage.

Add onions, garlic, and dried basil, stir to combine, and cook for 5 minutes.

Add mushrooms and stir to combine, cooking for another 5 minutes.

Stir in diced tomatoes, tomato paste, and pepper, bring to boil then simmer for 15 minutes.

Stir in spinach and cook until wilted. Remove from heat.

In a small saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute.

Whisk in milk and cook for 5 to 10 minutes until thickened; stir in ¾ cup mozzarella and salt.

Cook spaghetti in boiling water for 5 minutes, drain, then add to meat sauce.

Spread meat sauce in a casserole dish, pour cheese sauce over, top with remaining mozzarella and Parmesan.

Bake for 30 minutes until topping is golden and bubbly. Serve hot.