1. Preheat oven to 400 degrees F.
2. Peel and roughly chop 1 small yellow onion and set aside.
3. In a small bowl, mix ¼ cup olive oil, 4 minced cloves garlic, thyme and salt and pepper.
4. Slice lemon into thin slices then halve. Place the fish on their sides and carefully cut slits that are large enough to fit lemon slices against the grain of the scales. Place 4 lemon slices or as many as you can fit in the cuts.
5. Rub olive oil mixture on and inside of the fish, placing 1 crushed garlic clove and remaining lemon slices inside of the Branzino.
6. Place chopped onions inside the center of an If You Care Medium Roasting Bag seam side up on a baking sheet and then place the Branzino head first into the bag on a slight angle. Drizzle remaining olive oil mixture inside Roasting Bag and add the white wine.
7. Fold the open end of the bag tightly towards the top as many times as possible to seal.
8. Roast for 30-35 minutes. For a crispier fish, carefully cut open Roasting Bag to expose the top of the fish for the last 15 minutes of cooking.