1. Preheat oven to 425 degrees Fahrenheit. Prepare a baking sheet by lining it and spraying with pam.
2. Slice the onions into rings and place on baking sheet. Drizzle with a bit of olive oil and sprinkle with salt.
3. Roast the red onions until charred, approximately 10–12 minutes. Remove from oven to cool.
4. In the food processor, blend the onions with the light mayonnaise and lemon juice.