Add the vegan butter to a heavy bottomed pot and let it melt over medium heat. Add in the all purpose flour and stir it into a paste. 

Keep stirring and over the course of about 20 minutes (if you're on high heat) and around an hour on low to medium heat, you'll watch the roux change, from a thick paste into a thin sauce and the color will gradually change until you eventually reach a milk chocolate color which indicates that your roux is perfectly done. A high quality heavy bottomed pot will be ideal especially if you choose the high heat fast route. If you have a concern that it may burn in your pot then rather take the slow and steady approach. The end result will be worth it. 

If you burn the roux, you have to start again. So be very careful. Unfortunately once burnt that roux can't be salvaged and it will have to be redone. 

When your roux reaches the milk chocolate stage, then add in the green bell pepper, celery and onion, called the 'Holy Trinity' of veggies. Add to your roux and mix in and cook until the veggies are softened. 

Add the vegetable stock and stir in. 

Add frozen veg, cauliflower florets, mushrooms, garlic, cajun seasoning, liquid smoke and a bay leaf. Stir this in. 

Add the chopped tomatoes and kidney beans and stir in. Bring it all to a simmer, cover the pot and leave it to simmer until everything is cooked and fragrant. 

Add salt and pepper to taste. 

Serve with basmati rice (optional) with some chopped spring onions on top.