1. Preheat oven to 350°F; butter a 7-by-11-inch baking dish. In a large bowl, combine pretzels, oats, raisins and sunflower seeds.
2. Melt butter in a small saucepan over medium-high heat. Add peanut butter, sugar, honey, vanilla, flour and salt; stir until smooth.
3. Pour butter mixture into pretzel mixture and stir quickly to thoroughly coat. Transfer mixture to prepared baking pan and use your fingers to press in firmly and evenly. Bake until lightly browned, about 20 minutes. Cool completely in pan on a wire rack before cutting into bars.