Preheat oven to 450 degrees. Slice onion to 1/4” slices. In medium saucepan over medium-low heat, melt butter and add onions. Sauté for 10 minutes until softened and translucent.
Remove pizza from all packaging, and add onions and shredded Swiss cheese to the pizza. Place pizza directly on the oven rack and bake for approximately 15-20 minutes, or crust is golden brown.
Remove from oven and top with croutons and fresh thyme.