Preheat the oven to 400˚F (200˚C).
Spread the onion on a baking sheet and drizzle with the olive oil. Roast for 15 to 20 minutes, until the onion is slightly charred. Let cool to room temperature, then roughly chop and transfer to a medium bowl.
To the bowl, add the mayonnaise, sour cream, Hearty Seasoning, salt, and lemon juice and whisk to combine.
Serve the onion dip with chips.