Bring a large pot of water to a boil and season with salt. Add spinach and cook until wilted, about 2 minutes. Drain and immediately plunge spinach into cold water. Once cool, put spinach in a clean dish towel and squeeze out as much water as possible. You will need ⅓ cup tightly packed drained spinach.

In a food processor, combine spinach, eggs, 1 tablespoon oil, and a pinch each of salt and pepper. Process until smooth.

Oil a large skillet and set over medium heat. Ladle scant ⅓ cup of batter into skillet and quickly spread it out in a thin layer to coat base of skillet. You can do this by tilting the skillet. Cook until the top of crêpe is set, about 1 minute, then turn over carefully with a spatula and cook the other side for another 15-30 seconds. Remove to a plate and keep warm while you cook the remaining batter.

Heat 2 tablespoons of oil in a large skillet until shimmering. Add squash, salt, and pepper to taste and cook until tender, about 8-12 minutes. Remove from heat. Stir in grated lemon zest and mint.

Put some filling in center of each crêpe, dot with yogurt, if using, and roll up to serve. Eat immediately.