How to Make It
Bring 2 medium saucepans of salted water to a strong boil. Add the squid to 1 saucepan and the shrimp to the other and boil until just cooked, about 1 minute for the squid and 3 minutes for the shrimp. Drain the squid and shrimp and immediately transfer to a bowl of ice water to cool. Drain again and pat dry.
In a large bowl, mix the lemon juice with the peanut oil, parsley, cilantro, garlic and jalapeño. Add the mushrooms, shrimp and squid. Season with salt and pepper and refrigerate until chilled, about 10 minutes.
Meanwhile, using a sharp knife, peel the oranges, removing all the bitter white pith. Working over a bowl, cut in between the membranes to release the sections. Squeeze the juice from the membranes over the chilled seviche.
Arrange the orange sections and avocado wedges around the edge of a platter. Using a slotted spoon, spread the seviche in the center. Spoon some of the marinade over the oranges and avocados and serve immediately.