I use a food processor but you can do this by hand if you prefer that.
Remove the seeds in the chilli (or leave them in if you want it more spicy) and chop this finely in the food processor. You want nice small even pieces.
Put in the onion and scallion and mix that until the bits are fairly small.
Then put in the rest of the ingredients and mix until you get a consistency you like. I prefer it almost sauce like.