To properly cut a bell pepper, start by topping and tailing your bell pepper and laying it on its side. Do not through away the end pieces, you can use them in any number of applications, one of my favorite being tacos for family meal.
Slice downward through the flesh of the bell pepper and roll it out flat. In the same movement, as you are rolling out the bell pepper, run your knife along the inside of the flesh, almost as you would fileting a fish, and remove the seed pod completely.
From here, simply julienne and dice to the size necessary for your dish.
If you want to use a fine julienne bell pepper for garnish, lay flat skin side down, and remove the inner membrane. Julienne the remaining flesh as thin as possible. For a bit of extra drama, through in a container of ice water and let sit in your fridge overnight. The next day, you will find the thinly sliced bell pepper has curled into a beautiful, airy garnish.