Separate the stems from the leaves of the swiss chard. Reserve the leaves. Chop the stems and put them in a bowl. Add all remaining ingredients and yogurt, except the tortillas. Take each tortilla and put one swiss chard leaf in the center. Take 1/4 of salad mixture and place in the center of the swiss chard leaf, forming a line down the center of the tortilla. Fold in the long side of the tortilla, over the filling, then fold in two short ends and then roll everything over tightly onto the remaining end of the tortilla. Repeat with remaining tortillas to make a total of 4 wraps. Slice each wrap in half diagonally through middle. Serve.