1. To Make the Dressing: Put the lime juice, olive oil, mayonnaise, sour cream, cilantro, jalapeno, garlic, cumin, chili powder, and Parmesan in the container of a blender or food processor; process until smooth.
2. Refrigerate until ready to use.
3. To toast the pumpkin seeds: heat the olive oil in a small skillet and add the pumpkin seeds.
4. Toss continuously until the seeds are lightly toasted, about 3 minutes.
5. Season to taste with salt and let cool.
6. To Assemble the Salad: Combine the lettuce, onion, avocado, tortilla chips, and dressing in a large salad bowl.
7. Season to taste with salt and pepper.
8. Sprinkle the queso fresco and toasted pumpkin seeds over the salad.