Heat olive oil in a large skillet over medium heat. Add cauliflower, leek, carrot, and mushrooms. Cook until soft, about 10 minutes. Add sherry vinegar to deglaze the skillet. Increase heat to medium and whisk in flour. Cook for 7 minutes without browning the flour. Slowly whisk in soy milk and cook until thickened, 5 to 8 minutes. Reduce heat and bring everything to a simmer. Season with bay leaf, tarragon, thyme, oregano, mustard, salt, and pepper. Simmer for 20 minutes.
Preheat the oven to 375 degrees F (190 degrees C).
Combine flour, baking powder, and salt in a bowl. Gently mix in olive oil and water until a dough forms. Fold in olives.
Transfer cauliflower mixture to a 8x12-inch casserole dish. Drop biscuit dough on top.
Bake in the preheated oven until biscuit topping is lightly browned, about 20 minutes.
