COAT NUTS Adjust oven rack to upper-middle position and heat oven to 300 degrees. Line baking sheet with parchment paper and coat with cooking spray. Whisk egg white, lemon juice, lemon zest, and salt in large bowl. Add nuts and toss to coat. Drain in colander thoroughly, 4 to 5 minutes.
SEASON NUTS Mix brown sugar, minced rosemary, and red pepper flakes in large bowl. Add drained nuts and toss to coat. Spread nuts evenly on prepared baking sheet and bake until dry and crisp, 40 to 45 minutes, rotating sheet halfway through baking time. Cool completely. Break nuts apart and serve. (Nuts can be stored in airtight container for 3 weeks.).