Take 1 ½ cups of strawberries and place them in either a bowl or saucepan.
Mash them with the back of a fork. You could also puree them with a blender, food processor, or emulsion blender.
Add your strawberries to the saucepan (if they're not already in there).
Add sugar, cornstarch, and salt, and mix over medium heat until thickened. It can take a few minutes (up to 10 minutes).
Cool this mixture until it's just barely warm and add it to the rest of the fresh strawberries.
Mix well, but gently, before pouring this filling into the baked pie crust.
Chill in the refrigerator for an hour or two before eating. (This time frame depends on you and when you want to eat your pie. I'd recommend an optimal chill time of anywhere from 1 to 5 hours. But I've eaten the pie after 30 minutes of chilling and it was still amazing.)