I make a vegetable sandwich which I find very good. It has tomato, red onion, avocado, and cucumber. However, it lacks spiciness. I want to avoid spreads and use a vegetable for mild heat.  I tried an anaheim pepper. It has some kick but the texture does not work. It slides out. With the cucumber I cut them the length of the sandwich so they have structure.     Is there something with texture of cucumber but the spice of mild pepper?   
For this specific requirement I eat sliced cherry peppers in my sandwiches.  While they are not the length that you could cut cucumbers, I have little problem keeping them in the sandwich.  I have about as much trouble keeping tomatoes in the sandwich, and I rarely have to replace them. 