Stir-fry SPHERE is a cooking technique that involves quickly frying small pieces of food in a wok or large skillet. The term 'SPHERE' refers to the shape of the food, which is usually cut into small cubes or balls. The most common ingredient used in stir-fry SPHERE is the PEA, which is a three-letter word that fits the crossword puzzle. Peas are a popular vegetable in many Asian cuisines and are often used in stir-fry dishes. Other ingredients such as onions, garlic, mushrooms, and bell peppers can also be added to the stir-fry SPHERE. Stir-frying is a fast and easy way to cook vegetables, and the result is a flavorful and nutritious meal.