Peel and coarsely chop onion. Then, finely chop 1/4 cup and set aside for garnish
In a large frying pan over medium-high heat, warm 1 to 2 teaspoons oil until hot but not smoking. Add the coarsely chopped onion, season with salt and pepper, and cook, stirring occasionally, until starting to soften, 2 to 3 minutes.
Stir in the tomatillo simmer sauce base and bring to a boil, then reduce to a simmer.
Add the tortilla chips and cook, stirring occasionally, until starting to soften, 2 to 3 minutes.
Remove from the heat and season to taste with salt and pepper.
Meanwhile, prepare the lime yogurt and cilantro.