Coat a skillet with cooking spray. Place over medium-high heat until hot. Add onion and artichokes; saute until tender. Add spinach and 1/4 cup water; toss mixture lightly. Cover and cook 5 minutes or until spinach wilts. Uncover and cook until liquid evaporates. Add 2 tablespoons cheese; stir well.
Add water to a large saucepan to a depth of 2 inches. Bring to a boil; reduce heat, and maintain at a simmer. Break eggs, one at a time, into water. Simmer 7 to 9 minutes or until internal temperature of eggs reaches 160°. Remove eggs with a slotted spoon, and keep warm.
Place cornstarch in a saucepan; add milk, stirring with a wire whisk. Cook mixture over medium heat, stirring constantly, until thickened. Remove from heat; add lemon juice and next 3 ingredients. Stir with a wire whisk until smooth.
Remove crusts from bread; cut each bread slice in half diagonally, and toast. Place 4 bread triangles on each serving plate, and mound one-fourth of spinach mixture in center of toast, making an indentation in each mound of spinach with the back of a spoon. Place eggs in indentations. Top with sauce; sprinkle with remaining 1 tablespoon cheese.