Peel and devein shrimp and set aside. Steam the broccoli by putting in a glass bowl with 1 tablespoon of water and microwave for 2-3 minutes. Set aside. Heat oil in a large skillet or wok at a medium-high setting. Crush or mince garlic cloves and add to oil, being careful not to burn the garlic. Reduce heat to low and add the soy sauce, oyster sauce, broth and ginger. Bring the sauce mixture to a boil. Add in the shrimp and continue boiling until the shrimp cooks through--about 3-4 minutes. Add the steamed broccoli and water chestnuts. While stirring, add in the corn starch 1 teaspoon at a time until desired sauce consistency is achieved. Serve over rice or chow mein noodles.