Rinse and drain the amaranth grains.
Combine amaranth with 1 1/4 cups of salted water and bring to a boil. Lower heat, cover and simmer for 25 minutes.
Dice the bell peppers.
In a pan, on high heat, add the olive oil. Then, once hot, add the bell peppers, onion and corn. Sauté for about 5 minutes until the corn is cooked through. Toss with the cooked amaranth along with the fresh sage, lemon juice, salt and pepper. Refrigerate for at least 2 hours.