1. Place the lemon juice, salt, and about 3 cups of water in a 10" pan. Add the salmon fillets and more water to cover the salmon if necessary.
2. Turn the heat to medium and bring the liquid to a simmer. Remove the fillets when they are just opaque, about 2 to 3 minutes depending on thickness. Place the fillets in the refrigerator to cool. (This can be done in advance and kept covered in the refrigerator for up to 2 days.)
3. Flake the salmon into small pieces with a fork and set aside in a small bowl.
For the wraps:
4. Halve the cucumber lengthwise and scoop out the seeds. Cut it crosswise and then into julienne strips. Toss the strips with a tablespoon of the lime juice in a small bowl. Season with salt and pepper to taste.
5. In a small bowl, mix the cream cheese, onions and dill with the back of a fork into a paste.
6. Cut 1 inch off one side of each tortilla. Place all the tortillas on your work surface with the side that is still rounded facing you. Using half of the cream cheese mixture, divide it among the four tortillas, spreading it on the bottom edge. Top with the salmon, dividing it evenly among the tortillas. Top with the remainder of the cheese mixture. Divide the cucumber strips evenly among the tortillas. Roll up tightly ending with the cut side down.
7. You can make these ahead and chill them overnight, individually wrapped in plastic.
8. Slice in half on the diagonal and serve at room temperature.