Heat a large heavy-based pot on MEDIUM. Add in the olive oil and flour and stir with a whisk or rubber spatula. Continue for 15–20 minutes until it turns a beautiful caramel color.
Add the onion, garlic, mushrooms, green pepper, and celery to the pot. Sauté for 10 minutes.
Add the crushed tomatoes, vegetable stock, bay leaves, and Cajun spice. Mix well. Bring to a boil, turn down the heat, then let it simmer covered for 20 minutes. If the sauce gets too thick, add a splash of water.
Add the green beans, cauliflower florets, zucchini, and beans into the sauce. Stir well. Cook for another 10 minutes. Taste for seasoning. Add salt and pepper to taste. Stir in the green onions and serve.