Toast with Lemony Pea Mash

quartered

fresh

divided, plus more for toast

shelled, or frozen peas, thawed

chopped

finely chopped, from 1/2 preserved lemon, divided

or more

or crushed red pepper flakes plus more for serving

or ciabatta, toasted

Preserved, are lemons that have been soaked in salt and lemon juice for several weeks They are available at Middle Eastern markets and specialty foods stores