In bowl combine pineapple, tomato, onion, cilantro, jalapeno, garlic, cumin and salt. Stir several times while grilling to get the flavors to meld together.
Preheat grill to 400 degrees. Grill pork tenderloin until golden brown and cooked through; about 30 minutes. Turn several times. Remove from grill, cover loosely with foil and allow to rest for 10 minutes. Slice pork tenderloin and serve with pineapple salsa.
When storing leftovers separate the salsa from the pork tenderloin so the acids in the pineapple do not affect the texture of the pork tenderloin.