Flatbread With Avocado and Scallion Salsa

Name: Flatbread With Avocado and Scallion Salsa
Ingredients: 1 ½ tsp. sugar; 1 (¼-oz.) envelope active dry yeast (about 2¼ tsp.); 2½ cups (313 g) all-purpose flour; ½ cup whole-milk plain Greek yogurt; 2 Tbsp. extra-virgin olive oil; 2 tsp. kosher salt; 2 tsp. coriander seeds; 2 tsp. cumin seeds; 8 scallions; 4 Tbsp. plus 1 cup extra-virgin olive oil, divided, plus more for brushing; Kosher salt; 1 red or green chile (such as serrano or jalapeño), finely chopped; 1 cup finely chopped parsley; 1 lemon; 4 medium avocados, pits removed; Flaky sea salt (optional); Special Equipment: A spice mill