Spray the inside of your crockpot with non-stick cooking spray and set it aside.
On a plate, combine the flour and Montreal steak seasoning. Mix well.
Press each piece of steak into the flour mixture, coating both sides evenly. Shake off any excess flour and discard the remaining flour mixture.
Place the coated steak pieces in the crockpot.
Top the steak with the sliced onions and bell peppers.
Pour the canned whole tomatoes over the steak and vegetables.
Sprinkle the brown gravy mix evenly over everything in the crockpot.
Cover the crockpot with its lid and cook on low for 8-10 hours, or on high for 6-8 hours, until the steak is tender and fully cooked.
Once done, serve the Swiss steak hot, spooning the flavorful tomato gravy over each serving.