Meanwhile, thinly slice cucumber. Split buns in half and toast in oven or toaster oven until golden brown, 3-5 minutes. (TIP: Place the buns on a baking sheet first if you’re toasting them in the oven.) In another medium bowl, toss cucumber, mixed greens, 1 tsp white wine vinegar (we sent more), and a drizzle of olive oil. Season with salt and pepper.