To make the salsa, whisk together the juices, zest and oil in a large bowl and season with salt and pepper. Add the cucumber, jicama, onion and cilantro and mix to combine and taste for seasoning. Cover and refrigerate for at least 30 minutes to allow flavors to meld.
For the relish, put the avocado halves in a large bowl, add the lime juice and salt and pepper and coarsely mash with a fork. Fold in the onion, serrano and cilantro and gently mix to combine. Taste for seasoning, add more salt and pepper and if needed, a touch of honey.