Cook pasta as directed on package, adding bouillon granules to the boiling water along with the pasta instead of the salt. Drain pasta, reserving 1-1/2 cups of the pasta cooking water.
Cook bacon in medium skillet on medium heat 2 min., stirring frequently. Add sage; stir. Cook 3 min. or until bacon starts to turn crisp, stirring frequently. Remove bacon mixture from skillet with slotted spoon; drain on paper towels. Discard all but 2 Tbsp. bacon drippings in skillet.
Add onions to reserved drippings; cook and stir 2 min. or until crisp-tender. Add squash and garlic; cook 2 min., stirring frequently. Add reserved pasta cooking water; stir. Bring to boil; cover. Simmer on medium-low heat 8 min. or until squash is crisp-tender.
Remove 1/2 cup of the squash mixture; reserve for later use. Spoon remaining squash mixture into food processor container. Add 1/4 cup Parmesan; process until smooth. Return squash purée to skillet; stir in sour cream. Add pasta; mix lightly. Cook 2 min. or until heated through, stirring frequently. Remove from heat.
Top with reserved squash mixture, remaining Parmesan, bacon and sage.