In a 2-quart pot with a tight-fitting lid, bring the water to a boil. In a medium bowl, rinse the quinoa with warm water, pour off most of the water, then drain in a fine-mesh strainer. When the water boils, add the quinoa and bring it back to a boil. Reduce the heat to the lowest setting, cover, and simmer for 15 minutes. The water should all be absorbed, and small holes should have formed on the surface of the grain. Let stand, covered, for 5 minutes, to finish steaming.
In a large sauté pan over high heat, dry-toast the pumpkin seeds. Shaking the pan, move the seeds over the heat until they begin to pop. Remove from the heat and put them into a food processor or blender. Add the cilantro, garlic, jalapeño, salt, and cumin and process, scraping the sides down frequently, until all the ingredients are well minced. Gradually add the olive oil and lime juice, processing until smooth.
If serving immediately, stir the cilantro mixture, bell pepper, and scallions into the quinoa while still warm. Otherwise, chill the quinoa and add the remaining ingredients when it is cool.