Preheat oven to 375 degrees. Remove thick stems from broccoli. Remove outer green leaves from cauliflower. Cut or break broccoli and cauliflower into florets. Slice onion into thin slices. Cut peeled garlic lengthwise. Cut green onions into thin slices. Grate gruyere and parmesan cheese. In a large sheet pan, (I used a 9” x 15”) add broccoli and cauliflower florets. Sprinkle yellow onion slices, garlic and green onions over top. Evenly drizzle olive oil and balsamic over vegetables. Sprinkle with salt and pepper. Lay links of sausage on the vegetables one or two inches apart. Spread gruyere and parmesan cheese over vegetables and links. Sprinkle with optional seasoning of your choice. Bake for 30 minutes or until links are cooked through. If vegetable are getting too browned, cover with foil if needed. Remove foil in the last 5-7 minutes to brown the links. Remove from oven, sprinkle with fresh parsley and serve hot.