1.To make Hollandaise sauce, fill bottom of double-boiler part-way with water; make sure water does not touch top pan. Bring water to a simmer. In top of double-boiler, whisk together egg yolks, lemon juice and 1 tablespoon water.
2.Add butter to egg yolk mixture 1 or 2 tablespoons at a time, whisking constantly. If sauce becomes too thick, add 1 to 2 teaspoons hot water. Whisk until butter is incorporated. Whisk in salt; remove from heat. Cover pan.
3.To poach eggs, fill large saucepan with 3 inches water. Bring to a gentle simmer; add vinegar. Carefully break eggs into simmering water; cook 2 1/2 to 3 minutes or until whites are cooked and yolks are still soft in center. Remove eggs from water with slotted spoon; set on warm plate.
4.Meanwhile, cut SPAM® Classic into 4 (1/4-inch-thick) slices. In medium skillet, heat SPAM® over medium-high heat until lightly crisp.
5.Place English muffins, cut-side-up, on serving plates. Top evenly with spinach, SPAM®, tomato and poached egg. Drizzle with Hollandaise sauce. Sprinkle with chives, if desired. Serve immediately.