Begin by slicing the beef sirloin into thin strips, ensuring you cut against the grain for maximum tenderness. Next, chop the green bell peppers and onion into bite-sized pieces, and mince the garlic to release its aromatic goodness.

In your slow cooker, combine the thinly sliced beef, chopped peppers, onion, and minced garlic. Pour in the soy sauce and add the stewed tomatoes along with the beef bouillon. Stir to ensure the ingredients are evenly distributed.

Cover the crock pot with its lid and set it to cook on low for 6 to 8 hours, or on high for 3 to 4 hours. The beef will become tender and the flavors will deepen.

Once cooked, gently stir the mixture to combine and evenly distribute the sauce. Serve the Pepper Steak over fluffy white rice, creamy mashed potatoes, or alongside a fresh green salad.