Peel onions, cut into 1/4 inch slices; separate into rings.
Sift flour, baking powder and salt into medium size bowl. Stir in egg, water, lemon juice and melted margarine just until blended.
Dip onion rings in batter, a few at a time; fry in oil heated to 375 degrees (a cube of day-old bread will brown in 1 minute) about 2 minutes on each side.
Drain the golden rings on absorbent paper. Keep hot in a low temperature oven (325 degrees) until all are cooked.
The batter forms a crisp puffy envelope for this popular vegetable. There is archaeological evidence that onions (lily family) were cultivated more than 4,000 years ago. Onions, radishes and garlic were consumed in quantity by the laborers who built the Great Pyramid in Egypt.