Sprinkle gelatin over 2 tablespoons cold water in a small bowl; let stand 5 minutes. Add 1/4 cup boiling water, stirring with a whisk until gelatin dissolves; cool 15 minutes. Stir in onion and next 5 ingredients (through black pepper), stirring with a whisk. Chill 20 minutes or until mixture thickens.
Place cottage cheese in a blender; process until smooth. Add gelatin mixture and mayonnaise; process until well combined. Spoon cheese mixture into a large bowl; fold in salmon and chopped dill.
Coat a 4-cup loaf pan or metal mold with cooking spray; line with plastic wrap. Spoon salmon mixture into prepared pan; cover with plastic wrap. Chill overnight or until set. Invert pan onto a platter; remove plastic wrap.