Set a colander over a bowl. Add the zucchini and yellow squash to the colander and toss with 1 teaspoon of salt. Let stand for 20 minutes. Squeeze dry.
In a large, nonreactive skillet, heat the olive oil. Add the chopped red onion and season with salt and pepper. Cook over moderate heat until softened, about 3 minutes. Add 1/4 cup of the wine and cook until evaporated, about 2 minutes. Stir in the corn and 1/2 cup of water. Cover and cook until the corn is tender, about 4 minutes. Stir in the zucchini and squash and cook until heated through, about 2 minutes. Season with salt and pepper, cover and keep warm.
In a large, nonreactive saucepan, combine 2 cups of the wine with the lemon, thyme, bay leaf, the sliced onion, fennel if using and 2 cups of water and bring to a simmer. Season the Trout OR salmon with salt and pepper, add the fillets to the saucepan and cook at a bare simmer over low heat, turning once, about 6 minutes. Transfer the salmon to a plate and pat dry with paper towels. If using Skin on, peel skin off fish. Discard the poaching liquid. Keep the veggies and serve with the fish.
Add the remaining 1/2 cup of wine to the saucepan and bring to a simmer. Whisk in the butter, 1 tablespoon at a time, until thoroughly incorporated. Season with salt. Stir the basil into the poached vegetables and transfer to plates. Nestle the salmon into the zucchini and corn mixture, top with the butter sauce and serve.
Paired with La Storia Chardonnay
Adapted from Food & Wine annual cookbook 2010