Add the peas to a pot and cover with boiling water. Boil for 5 minutes or so until the peas are cooked. Rinse the cooked peas with cold water until cool and drain well.
Add them to a flat bowl and season with a generous pinch of salt. Add the zest of the lemon and about 2 tsp lemon juice. Finely chop the mint and add to the bowl. Mash everything together with a fork. Taste and add more lemon juice/salt if needed.
Spread over the toast, top with feta if using, a little bit more lemon zest and a sprinkle of chilli flakes. Enjoy!