Put a wok, cast iron or stainless steel on medium high heat and add oil. While oil is warming up, begin chopping onion, pepper and carrots and mincing the garlic.
When the oil is warm, brown the lamb. When the lamb is browned on all sides, remove from pan.
Add additional oil if necessary, then add onion, pepper and carrots to the pan. Saute until onion is soft and translucent, then add garlic and stir to release fragrance for about 30 seconds.
Return meat to the pot and add in spinach. Cook down until the spinach is mixed in and darkened.
Mix in teriyaki sauce and serve immediately.