1Beat together cream cheese, chopped dill and lemon juice.
2Line a 3 by 6 inch loaf pan with plastic wrap. Line the bottom of the pan with 1/3 of the lox.
3Spread 1/4 of the cheese mixture in an even layer over the lox.
4Cover with 1/3 of the lox and repeat layers, ending with lox.
5Gently press to even out layers. cover and chill until firm, at least 3 hours or up to 2 days.
6Lift terrine out of pan and remove plastic wrap. With a thin, sharp knife, cut terrine into 1/2 inch thick slices and place on salad plates along side crisp red onions and bagels. Garnish with dill sprigs.
7Crisp red onions: Thinly slice 1 medium red onion. Immerse in a mixture of 2 cups of water, 1/3 cup vinegar, and 2 cups ice cubes. Let stand until crisp - about 30 minutes. Drain and lift out onions.