Stir together mustard seeds, curry, ginger, cumin, and red pepper flakes, if using, in bowl; set aside.
Cook potatoes in boiling salted water 15 minutes, or until tender.
Drain, return to pot, and mash, leaving small chunks.
Heat oil in skillet over medium heat.
Add onion, carrot, and garlic, and sauté 5 minutes, or until carrot is tender.
Move onion mixture to side of pan, and add mustard seed mixture in center.
Toast 30 seconds.
Stir in peas and broth.
Fold onion mixture into potato mixture; stir in agave nectar.
Season with salt and pepper, if desired.