There are two variations to this and both are generally done off of a punch and practiced to the right side of the body of the person doing the throw.
First variation: From attacker punching, any appropriate block which opens up the person's mid section is generally applicable. So is any technique which can be used to get the person into a position where they are bending forward, generally with their right foot forward and closest to your body. This includes strikes such as Mae Geri, Ura Zuki, Chudan Seiken Zuke, etc. Once the opponent is bent over, position your legs so that the left knee is touching the opponent's right knee. Cup the back of the neck (if attacking for real, this may be a strike then a cup to pull back), then pull back on the next towards your right hip as you lean back. This should break the bubbling well point of their left foot. Then push straight forward from the neck and the lower back/hip with the left hand while collapsing the right knee in a shift forward, causing the person to roll out to their left.
Second variation: Again get your attacker into a forward leaning stance through any applicable means. Cup the back of the neck and press down as you sink and step straight back with the right leg. While pressing in a manner that would put the opponent's head between their legs, grip their right shin with your left hand and lift as you lift on the leg. With the momentum forward and down, the opponent should fall with a roll onto their back.