Combine soy sauce, honey, garlic, and dry mustard in a large resealable plastic bag. Add pork tenderloin pieces, coat with marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator at least 1 hour or up to overnight.

Preheat an outdoor grill for high heat and lightly oil the grate. Remove pork from marinade and shake off excess. Discard remaining marinade.

Grill on the preheated grill until seared and juices run clear, 4 to 5 minutes per side. An instant-read thermometer inserted into centers should read at least 145 degrees F (65 degrees C).