Merriam Webster says :
*any of various usually cold dishes: such as
a: raw greens (such as lettuce) often combined with other vegetables and toppings and served especially with dressing
b: small pieces of food (such as pasta, meat, fruit, or vegetables) usually mixed with a dressing (such as mayonnaise) or set in gelatin*
As such, even just cucumber would suffice.
Edit: in dutch, a "salade" has to accompanied by a dressing or vinaigrette, thus very much limiting what a salad is.