Drain the mandarins and collect the juice. Halve the tangerine pieces. Dilute the yogurt in a bowl with enough mandarin juice until the yogurt has a soup-like consistency. For me it is usually 2/3 of the juice. Then just add the tangerine pieces and serve.
Tip: If you like it a little sweeter, you can add powdered sugar, but I think it tastes better without it.