In a large bowl, make the portobello marinade. Combine the olive oil, balsamic vinegar, spices, and garlic.
Place portobellos and asparagus in a large oven-safe skillet. With a pastry brush, generously brush the marinade over the tops and bottoms of the mushrooms and asparagus.
Arrange mushrooms top side down and pour the remaining marinade over them. Bake for 20 minutes. Remove from oven, flip, and bake another 5–10 minutes or until mushrooms are cooked all the way through.
For Potatoes: Wash and peel the potatoes. Bring them to boil and cook until tender, about 15 minutes. Mash the potatoes using a potato masher or a hand blender. Add olive oil, black pepper, and salt, to taste. Add fresh herbs just before serving.