After the lentils are simmering measure the flour, baking powder and salt in a large bowl.
Make a well in the center and spoon the yogurt into it. Use a spoon to mix the flour into the yogurt until a loose dough forms, then use your hands to knead it until it forms a smooth mass (you can knead it right in the bowl). Cover and let rest until the lentils are finished.
When ready to cook the flat breads, dust your work surface with a little flour and turn out the dough. Knead it for a couple minutes, then portion it into 6 or 8 pieces.
Use a rolling pin to shape the pieces into thin rounds or ovals (about the thickness of a nickel), adding more flour as needed to prevent sticking.
Transfer the flatbreads to a tray and keep them covered to prevent them from drying out.
Heat a grill pan until very hot. Brush with oil or melted butter.
Transfer one or two flatbreads to the grill pan and cook. When the edges look a little dry and small blisters form on the top (one or two minutes), flip the flatbreads over to cook the other side. They may puff up when you turn them over. This is a good sign.
When cooked through, remove the flatbreads to a plate and brush with melted butter. Repeat for the remaining flatbreads.