Combine the coriander seeds and black peppercorns in a plastic bag and crush them with a heavy skillet or rolling pin until just cracked open (or use a mortar and pestle).

Mix in the vegetable oil and kosher salt to form a spice paste.

Spread the spice paste evenly all over the beef top sirloin roast.

Preheat the air fryer to 325°F.

Transfer the seasoned beef roast to the air fryer basket.

Cook at 325°F, turning the roast every 10 minutes, until golden brown and an instant-read thermometer inserted into the middle of the roast reads 125° to 130°F for medium-rare doneness, about 40 minutes.

Transfer the cooked beef roast to a cutting board and let it rest for at least 15 minutes.

Cut the rested beef into thick slices and serve warm.

If not serving immediately or to make sandwiches, wrap the cooled roast in plastic wrap and refrigerate until firm for easier slicing, at least 4 hours and up to 5 days.