Rinse spinach thoroughly, trim the ends of the stems and cut the leaves off the stems.Blanch spinach leaves for about 30 seconds in boiling salted water, then remove with a slotted spoon, rinse with cold water and let drain on paper towels.

Rinse scallions and cut into cubes.Rinse parsley and shake dry. Pluck the leaves from the stems and chop finely.

Meanwhile, rinse chicken breasts and pat dry with paper towels, then season with salt and pepper. Heat the canola oil in a pot and cook chicken over medium heat for 2-3 minutes on each side. Remove from pot.

Add spinach stems with the scallions to pot and cook for about 2 minutes over medium heat. Place in a bowl and let cool slightly. Stir in parsley and pesto. For each portion, place 2 overlapping spinach leaves on the work surface and generously spread with pesto mixture.

Put 1 chicken breast half on top and fold the spinach leaves over the chicken to make a packet. Repeat with remaining ingredients. Place spinach packets in a steamer basket set over a pot of boiling salted water, cover and cook over low heat for about 10 minutes. Serve with the tomato sauce.