1. Heat oil in skillet on medium-high. Add diced onions and sauté for five minutes, stirring constantly. Add the diced mushrooms and sauté for an additional 10 minutes while continuing to stir.
2. Add the garlic and seasoning and stir to combine, sauté for another minute or two.
3. Let the sautéed mushrooms cool slightly in a bowl. Add mayo and blend using a hand blender.