In the meantime, saute sausages (meat version) in a new skillet until browned. Or saute mushrooms in the first pan after vegetable mixture has been cooked.
Cut sausages in 1/2 inch round slices and place back in pan to further brown, 2-3 minutes. Remove and cool.
Layer sauteed vegetables, tomatoes, herbs, salt and pepper in a large casserole dish or two small ovenproof dishes. Stir gently to mix.
Return to oven and bake uncovered for 20 minutes.
Flavor improves by making the casserole 24 hours ahead and refrigerating. Bring to room temperature before reheating.