Heat a drizzle of olive oil in a large skillet over medium-high heat. Add the white and light-green scallion sections and jalapeño. Cook undisturbed until softened and charred in spots, about 3 minutes.
Flip the jalapeño and scallions and cook for another 2 minutes, then add the dark-green scallion sections. Cook for another 1–2 minutes, or until everything is softened and lightly charred. Cover the skillet briefly at the end, if needed, to help the jalapeño soften.
Transfer the scallions and jalapeño to a cutting board and let cool completely. Finely chop the jalapeño, removing the seeds first to reduce the spice level, and thinly slice the scallions. They will be slippery, so slice them carefully.
Add the scallions and jalapeño to a small bowl along with the olive oil, cilantro, lime juice, cumin, coriander, and salt. Mix to combine, then taste and season with additional salt as needed.
In a medium bowl, mash the avocados until mostly smooth. Stir in the yogurt, lime juice, salt, and garlic, if using. Taste and adjust the lime juice or salt as needed.
Transfer the avocado mixture to a wide, shallow serving bowl and use the back of a spoon to spread it into an even layer. Spoon the scallion salsa over the top.
Finish with pumpkin seeds, if using, a drizzle of olive oil, and a light sprinkle of salt. Serve with tortilla chips.