Slice the beef sirloin against the grain into thin strips.

Chop the green bell peppers and mince the garlic. Slice the onion if using.

Layer the sliced beef sirloin evenly at the bottom of the crock pot.

Add the chopped vegetables on top of the beef, placing the bell peppers and garlic first, and onion if using.

In a bowl, mix together the soy sauce and stewed tomatoes, then pour it over the layered ingredients in the crock pot.

Cover the crock pot and cook on low for 6 to 8 hours or high for 3 to 4 hours.

Once cooked, stir the Pepper Steak gently to coat with sauce, adjusting seasonings if necessary.

Scoop the Pepper Steak into bowls or serve with rice or mashed potatoes.