Place red pepper, pineapple, vinegar and sugar in the bowl of a food processor and process until smooth.
Transfer the mixture to a small saucepan and heat over medium high heat until it comes to a simmer.
Mix cornstarch with 2 teaspoon water until dissolved. Stir cornstarch mixture into the simmering pepper mixture. Simmer, stirring, for 1-2 minutes until the sauce has thickened slightly.
Taste your sauce and add additional brown sugar if you would like the sauce sweeter.