Try some roasted chilies. Maybe that'll work?

I would try basic white pepper.

... or maybe some ground radish.

I'd go for a milder chile like a jalapeño, I suppose. I don't know all that much about the subtle differences between peppers, but cayenne is rarely my go-to. I use it more for keeping squirrels out of the bird feeder.

I keep a bunch of peppers from my or others' gardens in the freezer. I think I have mostly serranos in there. I seed them and then chop. The veins are enough to make things spicy.

I'd be willing to bet that the "pinch" you used may have been too much? The one thing I do use cayenne for is a type of cheese cracker/cookie I make, and I find that just an eeeeensy bit goes a long way.

I like the roasted chile idea. Roasting adds a nice mellow flavor that I think would go well with avocado.

And I bet stewriffic's right - a 'pinch' might really need to be more like a teeny tiny hint, especially if you're fortunate enough to have strong (not old) cayenne.

Tabasco green.

Sriracha goes lovely with cucumbers.

What about wasabi? Or plain old horseradish? Just a tiny little hit to make your nose tingle...

Chipotle in adobo?

Cholula is a milder hot sauce.