Preheat oven to 375 degrees F.
On a small rimmed baking sheet, toss the red onion, olive oil, salt and pepper together. Roast in the oven for 25 to 30 minutes until the onion is very soft, stirring occasionally. Remove from oven and let cool. Transfer to a food processor and buzz until finely chopped. Add the mayo and pulse until smooth and combined.
Yield: 1 serving
Prep Time: 20 minutes
Cook Time: 25 to 30 minutes
Ease of preparation: easy