In a small bowl, combine the tamari, ginger, agave, Sriracha sauce (if using), 1 tablespoon water, and 1 teaspoon cornstarch. Set aside.
In a separate bowl, whisk together the egg whites, ¼ cup cornstarch, salt, and pepper. Stir in sesame seeds, then set aside.
Heat 2 tablespoons of oil in a large skillet over medium-high heat.
Dip a piece of chicken in the egg white mixture. Let the excess drain back into the bowl before placing the chicken in the hot skillet.
Repeat with each piece of chicken, being careful not to overcrowd (depending on the size of your pan, you may need to do two batches).
Cook the chicken until golden brown, about 4 minutes per side, then transfer to a plate and keep warm.
Heat remaining 1 tablespoon of oil in a wok or skillet over medium-high heat.
Add the white pieces of the bok choy and cook for about 3 minutes.
Add the red pepper and cook for about 2 minutes.
Add the green pieces of bok choy and cook about a minute.
Add the tamari mixture and cook until the liquid has thickened and the bok choy is tender, about 3 minutes.