Heat a small skillet over medium heat.
Add 2 tablespoons whole black peppercorns and 1 tablespoon whole coriander seeds to the dry skillet.
Toast, shaking frequently, until fragrant and slightly darker, about 2–3 minutes.
Immediately transfer toasted spices to a plate and let cool.
Grind cooled peppercorns and coriander seeds coarsely using a spice grinder or place in a zip-top bag and crush with a rolling pin.
In a small bowl, combine ground spices with 1 tablespoon garlic powder, 1 tablespoon onion powder, 1 teaspoon dried dill weed, 1 teaspoon red pepper flakes, and 3 tablespoons coarse kosher salt.
Stir until all ingredients are evenly distributed with no clumps.
Transfer seasoning blend to an airtight container and store in a cool, dark pantry for up to 6 months.