Heat the vegan butter (or vegetable broth) in a large skillet over medium-high heat.
Add the cauliflower florets and sauté for 5 minutes.
Add the mushrooms and continue to sauté for another 5 minutes, allowing the mushrooms to release their moisture. If the pan seems dry, add a few tablespoons of vegetable broth.
Reduce heat to medium and cover the skillet and steam for 3 minutes, or until the cauliflower is tender.
Uncover and continue cooking until any excess liquid evaporates.
Stir in the bell peppers and tomatoes, and cook for 2 minutes.
Add the garlic, all the spices, and the asparagus. Cook for 2 more minutes.
Pour in the worcestershire sauce, dijon mustard, lemon juice, and vegetable broth. Bring to a simmer.
In a small bowl, whisk together the cornstarch and water. Add this to the skillet to thicken the sauce.
Optional: if using, add the field roast vegan sausage to the sauce.
Simmer until the sauce reaches your desired consistency. Remove from heat.