If you're going to make your own peanut butter, start by there. Put the toasted peanuts without anything else in a food processor or a really good blender until it starts releasing its oils and becomes pasty.
In the same food processor add the rest of the sauce's ingredients and process.
Adjust the texture with water so that it's saucy.
Cut the chicken breasts in cubes, but don't make them too small. 3cm is fine.
Sear in a pan with vegetable oil and a few drops of sesame oil for that extra asian taste. Just put enough cubes so that the pan is covered with some space in between them. This way you know they will become golden. Add salt and pepper.
Once the chicken is done, add the pepper and cook it a bit with more oil. Add salt and pepper.
Make the lettuce wraps and enjoy!