Your favorite brunch special just took on a new, heartier format. Everything here comes through: The bagels, capers, lox, raw onions, and cream cheese are all balanced out by spinach's natural mild sweetness. This makes a lot of salad, so you could serve it as either a main or a side dish for a larger crowd. Using whipped cream cheese will make it easier to whisk. You can opt for hot smoked salmon, but cold is a classic. Since the spinach is hardy, you can make this up to 30 minutes before serving.