I always slow down, & talk to the horse. It seems to help them recognise me as a human being, not a scary zoomy thing. A former girlfriend of mine who had a horse recommended it, many years ago, & she was right. Speak early, too. They hear you coming long before their rider does. Watch, & you'll see their ears move when they first notice you.
But it doesn't always work. Some are spooked by anything, & I've never ridden a recumbent past one to see how they react to that.