Prepare the Roasted Jalapeños. Preheat oven to 425°F.
Place sliced jalapeños on a parchment-lined baking sheet.
Drizzle with oil and sprinkle with salt, pepper, and garlic powder.
Bake for 25 minutes.
Transfer peppers to a container and blend using an immersion blender.
Divide mixture into 4 ounce containers.
On the day of serving, thaw one container and mix with mayonnaise, salt, and lemon.
