Spray a 9-inch deep-dish pie plate with cooking spray.

In a medium bowl, stir together crushed pretzels, melted butter, and sugar. Press mixture into bottom and up sides of prepared pan.

Freeze until set, about 30 minutes.

In a large bowl, stir together condensed milk, lemonade concentrate, zest, and food coloring, as desired. Fold in 1½ containers whipped topping. Spread into prepared crust, smoothing top with an offset spatula. Freeze until firm, at least 4 hours or overnight.

To serve, let sit at room temperature for 10 minutes. Spread remaining whipped topping onto pie. Garnish with lemon and strawberries, if desired. Serve immediately.