Heat olive oil in a frying pan over med-high heat.

Brown tenderloin on each side (~10 minutes).

Mix together teriyaki sauce, chicken broth, brown sugar, garlic, pepper flakes, onion, and pepper in a medium bowl.

Place meat in slow cooker and coat in sauce.

Cook on high for 4 hours, turning 2-3 times throughout the cook time.

Remove meat from the slow cooker and let cool for 5 minutes before slicing. Spoon liquid over slices.