1 head garlic (about 12 to 14 cloves)
6 teaspoons olive oil (divided)
1 pound penne pasta
8 ounces bacon (about 8 slices) (cut crosswise into 1/2-inch-wide strips)
1 large onion (chopped, about 2 cups)
1 cup low-salt chicken broth
6 cups (packed) Treviso or Chioggia radicchio leaves, (coarsely torn, from about 2 medium heads)
3 cups (packed) Earthbound Farm Organic Baby Spinach (about 10 ounces) (torn in half)
1 cup freshly grated Parmesan cheese (plus more for serving)
1/4 teaspoon dried crushed red pepper flakes
  Salf and freshly ground black pepper to taste