Heat the cranberry and orange juice in a small saucepan, over medium heat until it boils. Remove from heat and let cool.
Strain cranberry mixture into a large bowl using a fine mesh strainer. Whisk in vinaigrette and sugar until well combined.
Add salad mix and half the dressing into a large bowl and toss with tongs until lettuce is coated. Add tomatoes and cucumber slices and gently toss. Add more dressing if necessary. Transfer to serving platter and top with croutons.