Cut asparagus into 2 inch long pieces. Try the roll cut: slice on a diagonal, then turn the spear one quarter turn and slice on the diagonal again.
Mix oyster sauce, soy sauce, water, cornstarch, and sesame oil until cornstarch is well dissolved. Set this seasoning sauce aside. Heat skillet to high and put a cup of water by the skillet (for thinning the sauce later if you need to).
Heat 1 Tbsp oil in a nonstick skillet set on high heat. Add shallots and asparagus. Stir the vegetables around for about 5-7 minutes. You are looking to get some nice browning on the edges. Taste a bit as you go to make sure they get tender, but still have a little bite. Remove from pan to a bowl or plate.
Heat 1 Tbsp oil and add mushrooms and some pepper. Stir mushrooms around on dry heat without adding any liquid. The mushrooms should shrink up and become browned.
Add asparagus back to pan. Turn heat down to medium. Add 1 Tbsp more of oil and add garlic and ginger. Once you can smell the garlic, quickly add seasoning sauce. Stir to coat all vegetables in sauce. The sauce will reduce rapidly. You can add another tablespoon or two of water if you need to distribute the sauce better.