Combine pumpkin seeds, cilantro, lime juice, chili powder, cumin, salt, and syrup in a high-speed blender and blend until smooth. Set aside.
For salad:
In a large saucepan, toast quinoa over medium heat. Stir often until you can hear continuous popping noises (about 6 minutes). Stir in water and 1/2 tsp sea salt. Bring to a simmer. Then, cover and reduce the heat to low until the water is fully absorbed and the quinoa is fluffy and soft (about 15 minutes). Transfer quinoa to a large bowl and let it fully cool.
Stir in peppers, corn, mango, beans, scallions, avocado (if using!), and dressing. Toss to combine.
To serve, top with more avocado and cilantro if desired.