Position rack in middle of oven and preheat to 375°F. Mist a large rimmed baking sheet with cooking spray. Mix oats, nuts, sunflower seeds, cinnamon and salt in a large bowl. In a saucepan, combine brown sugar, honey and oil and bring to a simmer over medium heat. Remove from heat; carefully stir in vanilla. Pour hot liquid over oat mixture, stir and toss until thoroughly mixed.
Spread granola on baking sheet and bake until golden brown, about 20 to 25 minutes, stirring occasionally to brown evenly. Transfer sheet to wire rack and let cool.