Rinse the amaranth and boil in lightly salted water for about 15 minutes, until tender. Rinse under cold water and drain well.
Rinse and dice the tomatoes. Peel the red onion and slice thinly. Cut the chile pepper in half lengthwise, remove the seeds and chop finely.
Rinse the parsley, pat dry and chop finely. Mix the corn oil, sea buckthorn juice, lemon juice and chopped parsley together. Add the amaranth, tomatoes, red onion and chile pepper to a large bowl, drizzle with the dressing and mix until well combined. Let stand for about 30 minutes before serving.