Season chicken with salt and pepper. Heat butter in skillet on medium heat, add onions and saute until limp (about 2 min.) Add to chicken.
Combine eggs, worcestershire sauce, tarragon, parsley, salt & pepper. Add to chicken mixture. Cook small portion of chicken to test and add more salt & pepper if required.
Heat chicken stock in skillet until simmering. Add leeks and spinach, and simmer uncovered until leeks are soft (about 5 min.) Drain very well.
Place leeks, spinach and garlic in blender with lemon juice, ricotta, beaten egg and breadcrumbs. Combine until slightly chunky, then stire in parmesan cheese and additional salt and pepper if desired.
Spread chicken on large sheet of waxed paper to form a rectangle 1/2" thick. Spread leek and spinach filling over chicken, leaving 1/2" border all around.
Roll chicken around filling using wax paper as a guide. Flip rolled chicken onto baking sheet, seam side down.
Combine soy sauce and maple syrup; brush chicken roll.
Bake at 350 for 45 minutes or until juices rise and are clear. Cool slightly and cut into slices.