Melt 1 tablespoon butter in large pan over medium heat. Add shaved red onion and cook 2-3 minutes. Transfer to bowl and set aside.
In same pan, cook chorizo until cooked through, breaking up into small pieces. Drain on plate covered with paper towels.
Split ciabatta loaf in half. Spread each half with 2 tablespoons butter (4 tablespoons total), then sprinkle evenly with garlic salt. Top bread evenly with Gouda, then add cooked chorizo. Top with squash shavings and cooked onion. Season with kosher salt and pepper. Broil in oven until cheese melts. Slice into individual pieces and garnish with fresh thyme leaves and serve.