Preheat oven to 375° F.

Cook macaroni according to package directions. Drain and set aside.

Heat oil in large nonstick skillet over medium-high heat.

Add onion and bell peppers; cook, stirring frequently, for 4 to 6 minutes, or until onion is translucent. Set aside.

Combine squash, broth, and milk in a medium saucepan. Bring to a boil over medium-high heat. Reduce heat to medium; gently boil for 22 to 25 minutes, or until squash is tender.

Place squash mixture in a blender or food processor; cover with lid and kitchen towel. Blend until smooth.

Combine squash mixture, macaroni, onion mixture, yogurt, and cheeses. Season with salt and pepper if desired; mix well.

Place macaroni mixture in a 13 x 9-inch ceramic or glass baking dish that has been coated with spray. Bake for 25 to 30 minutes, or until sauce is bubbling.

Garnish with parsley if desired.