Preheat an oven to 275 degrees F (135 degrees C). Cover a 10x15 inch pan with wax paper.
Mix brown sugar and water in a microwave safe bowl. Cook in microwave to dissolve the sugar, about 1 minute. Combine oats, salt, walnuts, and cinnamon in a large bowl. Stir in sugar mixture, honey, and vanilla extract. Mix well. Pour mixture onto the prepared pan, spreading evenly. Create clusters by squeezing small handfuls of the oat mixture together.
Bake in the preheated oven for 20 minutes. Remove from oven and gently stir granola using a spoon. Return to the oven and bake for an additional 25 minutes. The granola will be slightly browned and will continue to harden as they cool.
