In a large frying pan over medium-high heat, sautmushrooms with some of the olive oil for 2 to 3 minutes or until they are tender. Remove from heat.
Arrange cooked mushrooms evenly in one or two layers in a large baking dish. In a small bowl, combine olive oil, lime juice, garlic, parsley, shallots, white pepper, and salt; pour over mushrooms. In the refrigerator, marinate at least 4 hours or overnight.
Serve either cold or at room temperature. Plate on individual salad plates as an appetizer with 3 slices on the bottom at a diagonal and another 3 slices on top in the opposite direction (makes an appealing diamond pattern). Drizzle some of the marinade over the top, making sure you get some of the shallot and garlic.
Marinated Portobello Mushrooms Recipe: https://whatscookingamerica.net/portabellomarn.htm