Preheat oven to 300 degrees F. Line two 15x10x1-inch baking pans with parchment paper; set aside.
In an extra-large bowl stir together oats, rice cereal, pumpkin seeds, cheese, thyme, salt, and pepper. In a small bowl combine egg whites, oil, and Worcestershire sauce. Drizzle egg white mixture over cereal mixture; toss gently to coat. Spread mixture in the prepared baking pans.
Bake for 20 to 30 minutes or until golden, stirring occasionally. Cool on wire racks. Store in an airtight container at room temperature for up to 1 week.