Bring a pot of salted water to a boil and cook the whole wheat spaghetti according to package directions; drain and set aside.
Heat a large nonstick skillet over medium heat and spray with nonstick cooking spray.
Add the ground beef and cook, breaking it up and stirring frequently, until browned, about 5 minutes.
Add the chopped onion and garlic to the skillet and cook, stirring occasionally, until softened, about 5 minutes.
Stir in the chopped carrot and cook about 2 minutes, then add the chopped mushrooms and cook briefly to combine.
Add the canned diced tomatoes, tomato paste, dried basil, and dried oregano; bring the mixture to a boil.
Reduce heat to low, cover, and simmer for 10 minutes.
Uncover, stir in the skim milk, and continue to cook uncovered until the sauce thickens, about 15 minutes; season with salt and pepper to taste.
Divide the cooked spaghetti among 4 bowls and top each with the bolognese sauce; garnish with fresh basil if desired.
