Bring a large pot of water to a boil over high heat. Add the sweet potatoes and simmer until fork tender (but not mushy), about 20 minutes. In the last 3 to 4 minutes add the edamame and corn. Drain and set aside to cool.
In a large salad bowl whisk together the yogurt, oil, mustard, lemon juice, salt, and pepper. Add the red pepper, shallot, cilantro or parsley, and pumpkin seeds.
Allow the sweet potatoes to cool then chop into 1/2-inch cubes and add to the bowl along with the edamame and corn. Toss until well combined.
Taste and add more salt and pepper, if needed. Serve at room temperature or chill in the fridge until ready to serve.
Store leftovers in an airtight container in the fridge for up to 3 days.