Mix all the spices together in a bowl, and reserve them for later use.
Wash the sirloin tip roast to remove any blood, and pat it dry with a clean cloth or paper towel.
Lightly season the roast with a sprinkling of salt. Liberally coat the entire roast with the coffee rub mix. Optionally, leave the rubbed roast in the fridge overnight to transfer more flavor.
Season the roast with a sprinkling of salt, and roughly julienne the Spanish onion. Spread the onion on a roasting tray as a bed for the roast.
Preheat the oven to 400F and place the roast on the roasting tray.
Cook the roast in the pre heated oven, uncovered for 15 minutes, then drop the temperature to 325F and continue cooking for 20 minutes per pound of meat. For a 4 lb roast the roast would be in the oven for 1 hour and twenty minutes total for medium rare.
Remove the roast from the oven and let it rest covered with tinfoil for at lest 10 minutes.
Let the roast rest before slicing for at least 10 to 15 minutes. Cover the roast during this time to keep it warm.
Remove any juices from the roasting tray, and thicken them to make a pan gravy, or simply add the juices to a pre-made gravy.
Slice the sirloin tip roast, and serve with suitable sides.