In a mortar and pestle, combine Whole Whole Coriander Seeds (3/4 teaspoon), Fennel Seeds (1 1/4 teaspoon), and Crushed Red Pepper Flakes (1/2 teaspoon). Use the pestle to crack and grind the spices in the mortar until the spices are crushed and fragrant.
In a small bowl, add the Fresh Rosemary (1 1/2 tablespoon), Garlic (3 clove), Kosher Salt (1 1/2 teaspoon), Ground Black Pepper (3/4 teaspoon), and crushed spices. Stir to combine.
Place the Pork Tenderloin (1 pound) on a baking sheet and rub Olive Oil (1 tablespoon) over it with your hands. Sprinkle spice mixture over the pork and rub it in. There should be enough spice to liberally cover the entire tenderloin.
Cover loosely with plastic wrap, and refrigerate at least one hour or up to 8 hours.
Heat your grill to a medium-high heat (about 425 degrees F or 220 degrees C). Grill pork turning occasionally, 12-15 minutes for medium or until desired doneness is achieved.
Let the meat rest for 5 minutes then slice and serve.