Put the chopped onion, ginger, garlic, and 4 tablespoons of the lemon juice in the container of the electric blender, and blend at high speed to get a smooth paste (about 1 minute). In a bowl or pot with nonmetallic lining large enough to hold the meat, put the paste from the blender and all the other ingredients except the meats and the onion is to be used for garnishing later. Mix well. Carefully cut off all fat and tissue from the meat, and with the point of a knife make lots of in it into 2 pieces, if there is not room. Make a few more jabs with the knife, and be sure the paste gets rubbed into the meat and goes way inside the gashes. Cover the container and leave refrigerated for 24 hours. Turn the meat over at least 3 or 4 times during this period. The meat is now ready for grilling. But before you start, get your garnishes ready. Peel the second onion and slice it into very fine rounds (paper thin if possible). Separate the rounds into rings and put them into a bowl of ice water, cover, and refrigerate. Cut off the stems, leaves, and tips from the radishes and then cut them into flowers. (Starting from the tip end, start cutting into halves, but stop short as you reach the stem end. Next, cut into quarters and eights the same way.) Put into a small bowl of ice water, cover and refrigerate. It will look prettier if you use unblemished radishes of approximately the same size for this. Get fire started. When hot, place the metal grill at the lowest notch. Lift meat from bowl leaving marinade and place on grill. Sear 5 to 8 minutes on either side. Then raise grill to its topmost notch and cook about 20 minutes on each side. Brush frequently with the marinade until it is all used up. If you don't have a grill that moves up and down, just remember that the meat needs to cook about 50 minutes and it should be very dark on the outside and pinkish inside. To serve: warm a large platter. Meanwhile place the meat on a carving board and slice it as you would a London broil-into thin diagonal pieces. Drain off water from the radishes and onion rings. Arrange radishes around meat and lay raw onion rings on top of meat.